Acetogenesis is mainly characterized by the formation of acetate. It is the process of forming acetate by acetogens through a variety of metabolic pathways including homoacetate fermentation, mixed acid fermentation and propionic acid fermentation.

Acetogens are bacteria that produce acetate as their sole end product from certain sugar fermentation. Acetobacterium species, Clostridium aceticum and C. thermoaceticum are typical examples of acetogens.

Acidophiles are microorganisms that grow best at low pH (e.g. 3). They grow optimally between pH 0 to 5.5 (acidic).

Acrasiomycetes are cellular slime moulds.

Activation energy is defined as the energy required bringing substrates together at the catalytic sites of an enzyme so that they can reach their transition state.

Active carrier are individuals who has an overt clinical infection (i.e. disease with obvious signs and symptoms), and who can be a source of transmission of the pathogen to other individuals in a given population.

Active sites are the compartments found on the surfaces of enzymes on which substrates are bound specifically. This site can also be called the enzyme’s catalytic site.

Active transport is the transportation of solute molecules across the cell membrane of an organism against an electrochemical gradient.

Acute diseases are diseases that have a rapid beginning but which persist for a relatively short period of time. They are diseases which develop rapidly and can be dangerous and cause fatality.

Adaptive immunity which can also be called acquired resistance to infection is an antigen-specific type of immunity that is an acquired ability of a host immune system to recognize and destroy specific microbes, their products and other foreign bodies that invade the body. It is a specific type of immune response that is elicited based on the previous exposure of a host to a particular pathogenic microorganism or antigen.

Adherence is the process by which pathogenic bacteria attaches itself to the body surfaces of its human host.

Adjuncts are substances that are usually added during beer production to increase and improve the alcoholic content of the beer.

Adjuvants are substances that increase the immunogenicity of an antigen and thus enhance immune response to them.

Adsorption is the physical binding of cells to a carrier molecule. It is the first example of cell immobilization technique and it is commonly used due to the ease to reverse the reaction.

Aero microbiology is the branch of microbiology that concerns itself with the study of the role of microorganisms in the air and in the contamination and spoilage of food, wine and beverages.

Aerobic bacteria are bacteria that grow in the presence of oxygen.

Aetiology is the scientific study of the origin and causes of infectious diseases.

Affinity is the binding strength between a single receptor site on an antibody and a single epitope on an antigen.

Aflatoxins are potent and harmful toxins produced by Aspergillus flavus.

Agar or agar-agar is the solidifying agent of culture media.

Agglutination is defined as the process in which antibodies known as agglutinins react specifically with antigens to form clumps. It is the visible clumping of particulate antigens by antibodies. It occurs with erythrocytes or red blood cells (RBCs). This is the basis for most of the in vitro latex agglutination test performed in the laboratory.

Agglutinins are antibodies that cause visible clumping of particulate antigens.

Air quality is defined as the degree to which the ambient air in a particular environment is pollution-free.

Algae are phototrophic eukaryotic microorganisms that are capable of carrying out photosynthesis.

Algal bloom is a rapid increase in the population of algae in a particular water system; and it result when water temperatures are warm and when nutrients, such as nitrogen and phosphorus, are present in the water.

Algicides are antimicrobial agents that kill algae.

Algology is the study of algae.

Alkaline phosphatase is an enzyme produced by organisms such as E. coli and the intestinal tissue of calf, and which removes the phosphate group that is present at the 5′ end of a DNA molecule.

Alkaliphiles are microorganisms that grow at very high pH levels (e.g. 9 and above). They are usually found in environments that are highly alkaline in nature (e.g. high-carbonated soils); and they can also be called alkalophiles.

Allergens are substances (allergenic substances) that provoke hypersensitivity reactions or allergy in an individual. They include dust, pathogens, foods (e.g. nuts, egg and milk, sea food and some beans), venoms of some insects such as bees and wasps, drugs (e.g. penicillin and sulphonamides), animal hairs and even pollen grains from some flowers (e.g. poison oak plant).

Alloantigens are unique antigenic molecules found on the surfaces of host cells and they vary among the individual members of a given species. They are antigens that are found in another member of the host’s species; and these antigens are capable of provoking an immunological response in the host.

Allotypic determinants are antigenic determinants mainly found in the constant regions of immunoglobulins. They are also known as allotypes.

Alpha haemolysis is the partial lysis of red blood cells (RBCs).

Amebiasis (amebic dysentery) is a parasitic disease that is characterized by abscesses in the liver and ulcers in the intestines; and it is caused by Entamoeba histolytica.

Amensalism is an adverse microbe-microbe interaction in which the product or activity of one microorganism has a harmful effect on another microorganism. It is a relationship in which the product of one microorganism or organism has a negative effect on the survival of another organism.

Ammonification is the mineralization of organic nitrogenous compounds such as ammonia or ammonium (NH4+) into inorganic compounds.

AmpC enzymes are broad-spectrum beta-lactamase enzymes that are usually encoded on bacterial chromosome, and which are active on cephamycins (e.g. cefoxitin and cefotetan) and oxyimino-β-lactam agents.

Amphibolism is simply defined as the combination of catabolism and anabolism. It is usually used to describe the metabolic pathway that participates in both anabolic and catabolic reactions.

Amphitrichous flagellation is a type of flagellation found in bacterial cells with single flagellum at each end of the cell.

Amylase (Starch hydrolysis) test is a biochemical test that is used to identify bacteria that hydrolyze starch (including amylopectin and amylose) with the help of the enzyme amylase. It is an enzyme that hydrolyzes or breakdown starch into maltose, glucose, and dextrin.

Anabolism is the processes by which energy and raw materials are used to build new macromolecules (e.g. nucleic acids and proteins) and other cellular structures during biosynthetic activities in the cell.

Anaerobes are microorganisms that thrive in the absence of oxygen.

Anaerobic bacteria are bacteria that grow in the absence of oxygen; and they thrive more in the presence of carbondioxide. Some bacteria can grow either in the presence or absence of oxygen, and thus are called.

Anaerobic digestion is simply defined as the anaerobic breakdown of complex materials of animal or plant origin to simpler substances by microbes. It is the process in which complex organic matter are completely degraded to a mixture of solid and gaseous end products in the absence of oxygen and with the help of a diverse community of microorganisms especially methanogenic bacteria and archaea.

Anaerobiosis is a condition in which there is absence of oxygen.

Anamorphs are fungal organisms with asexual characteristics.

Anaphase is the third stage of mitosis. It is the stage of mitosis in which each of the sister chromatids move in opposite direction towards the ends of the spindle pole as the centromere of each chromosome splits into two.

Anthrax is an infectious disease caused by the bacterium Bacillus anthracis. It is usually transmitted through the ingestion of the spores produced by B. anthracis.

Anthroponosis are infectious diseases whose pathogen are usually maintained in a human reservoir and which can be contracted by susceptible human or animal hosts.

Anthropophilic fungi are dermatophytes that naturally reside on the body of humans example includes Epidermophyton species and Trichophyton species); and they cause infection following the destabilization of the body’s normal flora.

Antibacterial agents are antimicrobial agents that kill or inhibit the growth of bacteria.

Antibiogram is the pattern of sensitivities of a given pathogenic microorganism towards an array of antibiotics (that are usually impregnated in a paper disk). It can also be called antimicrobial susceptibility testing.

Antibiotic resistance is a phenomenon that occurs when bacteria are not killed or inhibited by usually achievable systemic concentration of an antibiotic (drug) with normal dosage schedule and/or fall in the minimum inhibitory concentration ranges of the drug in question. It is the ability of bacteria to resist the killing or inhibitory effects (onslaught) of an antibiotic.

Antibiotic selective pressure is defined as the impact of antibiotic usage on a population of microorganisms – in which the microbes that are resistant to the antibiotic gain (or acquire) a survival advantage over those bacteria that are susceptible to the antimicrobial onslaught of the drug.

Antibiotic stock solution is defined as a concentrated solution of an antimicrobial preparation that will be diluted to some lower concentrated solution for actual use.

Antibiotics are substances produced by a microorganism (wholly or partly by chemical synthesis), which in low concentrations kill or inhibit the growth of other microorganisms

Antibodies are protein molecules produced by the immune system on exposure to an antigen, and that can combine specifically with foreign molecules.

Antibody-dependent cell-mediated cytotoxicity (ADCC) is a cell-mediated reaction in which nonspecific cytotoxic cells that expresses Fc regions (i.e. crystallizable fragment portion of an immunoglobulin) such as macrophages and natural killer (NK) cells recognize and bind antibody on a target cell and subsequently cause the lysis of the target cell.

Antibody-mediated immunity (AMI) is an acquired or adaptive immunity that is generally mediated by immunoglobulins or antibodies and B lymphocytes. It is also known as humoral immune response; humoural immune response mainly protects against extracellular bacteria, toxins and other extracellular foreign molecules.

Antifungal agents are antimicrobial agents which kill or inhibit the growth of fungi.

Antigen presentation is the sequence of immunological reaction involved in the display of antigenic peptide molecules complexed with MHC molecules on the surfaces of antigen processing cells (APCs).

Antigen presenting cells (APCs) are specialized cells of the immune system whose main function is to ingest, process, and present processed antigens in association with any of the MHC molecules to specific arms of the immune system especially the T lymphocytes for further immunological response.

Antigen processing is the immunological process involved in the digestion or breakdown of antigenic molecule to release peptide molecules that are associated with MHC molecules and presented on the surfaces of the infected host cells for presentation to effector lymphocytes particularly the T cells. It is the series of immunological events that is mainly involved in the formation of antigenic peptide molecules complexed with MHC molecules (Class I and Class II MHC molecules inclusive) for rapid immunological response.

Antigen-antibody reaction is an immunological reaction in which a particular antibody molecule reacts with a specific antigen to form an antigen-antibody complex which is marked for further immunological response by other components of the immune system.

Antigenic drift is the minor change that occurs in the antigenic structure of a disease-causing agent that allows it to evade attack by the immune system of a host in the course of an infection. It is a mutational alteration in the surface proteins (which are target sites of antibodies) of pathogenic strains of microorganisms in such a way that antibodies that recognizes these antigenic sites do so less effectively or no longer recognizes them as it used to previously.

Antigenic shift is a major change in the antigenic structure of a pathogen that gives it the exceptional ability to be unrecognized by the immune system of a host. It is a mutational change in the antigenic structure of a microbe that allows it to change from one antigenic type to another and thus continue to remain unnoticed by the immune system mechanisms of a host.

Antigenicity is the property of an antigen that allows it to react specifically with the product of the specific immune response (i.e. antibodies or receptors of T cells).

Antigens are molecules or substances that are foreign to the body (i.e. it is unknown by the host immune system).

Antimicrobial agents are natural or chemical agents that are used to either kill or inhibit the growth of pathogenic microorganisms. They are chemical agents that are selectively toxic against pathogenic microorganisms but do not harmfully affect the recipient host cells. Antimicrobial agents can also be called chemotherapeutic agents or antibiotics.

Antimicrobial stewardship is defined as the judicial or rational use of available antimicrobial agents in such a manner that limits the emergence and spread of drug-resistant pathogens.

Antiprotozoal agents are antimicrobial agents which are used to treat diseases caused by protozoa.

Antisepsis is defined as the process of killing or inhibiting the growth of microorganisms on animate (or living) things such as the human body.

Antiseptics kill or inhibit the growth of pathogenic microorganisms in or on living tissue. They are used to prevent sepsis or putrefaction (i.e. decay) on living tissues such as in wound infections.

Antiviral agents are antimicrobial agents which inactivate viral agents.

Anuria is a cessation of urine flow.

Apoenzymes are the protein components of enzymes. They can also be called apoproteins.

Apoptosis is defined as programmed cell death. It is a cell death that occurs by a biologically-controlled intracellular process that involves the fragmentation and cleavage of the host cells nucleic acid (particularly the DNA).

Appertization is simply defined as the heat-treatment of food at certain temperature levels that inhibit or kill pathogenic microorganisms present in the food. It is a method of food preservation in which certain types of food are exposed to lower temperatures (e.g. 40oC) which renders the food safe for consumer. Such food or food products are microbiologically stable for extended periods of time on subsequent storage. Appertization is another food preservation technique that is similar to pasteurization; and it is also employed in food industries to extend the shelf life of food products and thus limit microbial activities in them.

Applied microbiology is the application of the knowledge of microbiology (i.e. understanding of microbes) to solving tangible or practical problems in the society.

Aquifers are defined as underground layers of rock that are saturated with water that can be brought to the surface of the earth through natural springs or by pumping using machines.

Archaea are prokaryotes that live in extreme live conditions and they include the methanogens.

Artificially acquired active immunity is the immunity acquired by an individual after immunization or vaccination. In this type of immunity, the individual is given antigen preparations through injections; and this antigenic preparation (which is generally known as vaccines) is expected to spark the generation of numerous amounts of antibodies as well as effector lymphocytes that will protect the recipient host against any future exposure to pathogenic microorganisms.

Artificially acquired passive immunity is the immunity acquired when an individual is administered with specific antibodies or serum preparations containing specific antibodies or lymphocytes generated in another animal (e.g. horse). This type of immunity may spark allergic reactions in the recipient host since the antibodies are being generated from animal origin.

Ascariasis is a parasitic disease that is caused by intestinal roundworms or nematodes in humans.

Ascomycetes are fungi that reproduce sexually via the formation of endogenous ascospores (i.e. sexual spores) normally enclosed in a sac known as the ascus sac. Fungi in this division or class are commonly known as sac fungi because of their shape.

Ascospores are sexual spores formed by ascomycetes within a sac known as ascus. They are the sexual spore of a fungal organism (especially the ascomycetes).

Ascus is the sac-like fungal structures containing 4 or 8 ascospores. They are mainly formed by the ascomycetes.

Aseptic technique refers to all the quality control and precautionary measures taken by microbiologists in the laboratory in order to ensure that all working apparatuses are germ-free. They help to prevent contamination in the microbiology laboratory. It refers to all the precautionary measures taken during an experiment to avoid contamination of the work and the researcher.

Asporogenous bacteria are organisms that do not produce spores.

ATPase is the enzyme that brings about the hydrolysis of ATP to ADP and inorganic phosphate (Pi).

Atypical Mycobacteria are non-tuberculous Mycobacteria that are also members of the human normal microflora, and which can be found in water surfaces. They are generally non-contagious in nature.

Autoantibodies are antibodies produced against the host cells or tissues to cause autoimmune diseases.

Autoantibody is an antibody produced by the body, and directed against normal body tissue. It results when autoimmunity sets in.

Autoimmune disease is a malignant and often fatal disease condition caused as a result of the activation of autoantibodies against the normal tissues of the body. It is the self-inflicted immune system disease caused by host molecules. They are diseases caused by an attack of the immune system on an individual’s own body tissues (i.e. self-molecules). They are diseases that arise due to the malfunctioning of the immune system.

Autoimmunity is the process by which the body mounts an immune response against a normal body component.

Auto-inducers are cellular signaling molecules produced by microbes (particularly bacteria), and which give them the exceptional ability to direct and monitor gene expression in their immediate environment.

Autosomes are chromosomes that are not sex chromosomes, and they include the 22 pairs of body or somatic cells of a normal human cell.

Autotrophs are organisms that can manufacture their own food; and examples include green plants and green algae.

Autotrophs are organisms that utilize carbondioxide (CO2) as their sole source of carbon.

Avidity is the overall strength of binding or interaction between an immunogen with many epitopes and a polyvalent antibody (e.g. IgM).

Axenic animals are laboratory controlled animals that are germ-free i.e. animals that are not contaminated with any microorganisms and are devoid of any microflora. They can also be called gnotobiotic animals.



B cells are lymphocytes whose most important function in the immune system is to secrete antibody-producing plasma cells following their specific interaction with antigens or foreign body. They are the main mediators of the humoural immune system. They are specialized type of lymphocytes that are responsible for the production of antibodies or immunoglobulins that act as effector molecules to stimulate the entire immune system against an invading antigen or pathogen. They are primarily responsible for the development of antibody mediated immunity (AMI) in the body.

Bacteraemia is defined as the presence of bacteria in the blood.

Bacteria are unicellular prokaryotic organisms with varying shapes and sizes including cocci (spheres), rods (bacillus), spirals (Spirillum), and coccobacillus (i.e. curved or bent rods). They are prokaryotes not found in the domain Archaea.

Bactericidal agents are antimicrobial agents that kill bacterial cells. They are antibiotics that can kill bacteria.

Bacteriology is the study of pathogenic bacteria.

Bacteriophages are viruses that infect bacterial cells or prokaryotes. They can also be called phages. They are viruses or viral particles whose host is a bacterium.

Bacteriostatic agents are antimicrobial agents that inhibit the growth of bacteria. They are antibiotics that inhibit the growth of bacteria.

Bacteriuria is the presence of bacteria in urine.

Baffles are structures that are connected to impellers and they help to eliminate the formation of vortexes in the fermentation medium.

Basidiomycetes are fungi that form sexual spores known as basidiospores. The basidiospores which are usually four in number are generally carried on a club-shaped structure known as the basidium; and fungi in this class or division are also known as club fungi because of their shape.

Basidiospores are sexual spores formed at the end of the basidium (a club-shaped structure) by basidiomycetes.

Basophils are granulated white blood cells (WBCs) or leukocytes; and they usually contain vasoactive substances such as histamine produced during allergic reactions in the body and heparin, an anticoagulant.

Batch culture is a closed system of cultivation of microorganisms in which nutrients are only added at the beginning of the culture process. There is no continual addition of nutrient to this type of culture as the nutrient level is depleted. In batch culture, microbial cells experience four (4) types of growth including: lag phase, log or exponential phase, stationary phase and the decline or death phase.

Batch fermentation is defined as the liquid fermentation process in which the culture is inoculated into a sterile medium contained in a closed vessel. It is also known as a closed-culture system.

Beer is an alcoholic beverage that is produced industrially by the microbial fermentation of wort (sugary solutions obtained by the dissolution of malted cereal grains).

Beta haemolysis is the complete lysis of red blood cells (RBCs).

Beta-lactam antibiotics are group of naturally-synthesized antibiotics that inhibit the synthesis of cell wall in bacteria.

Beta-lactamases are enzymes secreted by both Gram positive and Gram negative bacteria, and which have the ability to hydrolyze (breakdown) beta-lactam antibiotics including penicillins, cephalosporins and carbapenems.

Bias is a systematic error hat results in an unfounded or incorrect estimate of the measure of relationship between the cause and effect of a disease.

Binary fission is a cell division in which the parent cell or organism divides into two equal parts to form two daughter cells.

Binomial nomenclature is the system of classification that assigns two names to an organism i.e. the generic name and specific or species name.

Bioaerosols are microbial suspensions or airborne particles produced by microbes including fungi, bacteria and viruses, and which are mainly found in the atmosphere.

Bioattenuation is the method that relies on natural processes to dissipate contaminants through biological transformation.

Bioaugmentation is defined as the practice of adding actively growing, specialized microbial strains or cultures into a microbial community in an effort to enhance the ability of the microbial community to degrade certain compounds in a given environment.

Bioavailability of a drug is the actual portion of an administered drug that reaches the systemic or entire circulation of the recipient host in a chemically and effective unchanged form.

Biochemical (biological) oxygen demand (BOD) is defined as the amount of dissolved oxygen that is required for the microbial oxidation (decomposition) of soluble, biodegradable organic matter in an aquatic environment.

Biochemical tests are series of experiments that can be used to differentiate bacteria based on their metabolic activity or ability to utilize a given substrate such as glucose.

Biodegradation is defined as the degradation of a substance or material as a result of biological (usually microbial) activity. It is the decaying of all organic materials is carried   out by a complex and diverse community living organisms that comprise mainly bacteria and fungi, and other organisms.

Biodeterioration is defined as the deterioration (spoilage) of an object or material as a result of biological activity (usually microbial activity). It is the undesirable change in the physical and/or chemical properties of a material that is caused by the activities of living or biological organisms including microbes.

Biofertilizers are as preparations containing living cells or latent cells of efficient strains of microorganisms that help crops or plants to take-up nutrients from the soil through their interactions in the rhizosphere (microecological zone in direct proximity of plant roots) when applied through seed or soil.

Biofilms are well-organized microbial systems consisting of different layers of microbial cells associated with surfaces, and that possess complex structural and functional characteristics.

Biogenesis is the hypothesis that living organisms originated from pre-existing living things.

Biogeochemical cycling is a pathway through which chemical substances including carbon, nitrogen, phosphorus, calcium, water, oxygen and sulphur are cycled through the biotic (living) and abiotic (non-living) components of the earth.

Bioinformatics is simply defined as the application of information technology (e.g. computational tools such as computers) in the analysis, storage, recovery, manipulation, interpretation and distribution of biological data.

Bioleaching is simply defined as the solubilization of metals from their ores using microorganisms. It is the dissolution of metals from their natural mineral sources or ores by certain group of naturally-occurring microbes known as bioleaching microbes.

Bioleaching microbes are special class of microorganisms that “eat rocks” and facilitate the process of bioleaching. Typical examples of bioleaching microbes include Thiobacillus species, Leptospirillum ferrooxidans, Acidithiobacilus thiooxidans, Sulfobacillus acidophilus, thermophilic bacteria and heterotrophic bacteria and fungi (which require organic supplements for growth and energy supply) are some notable examples of bioleaching microbes.

Biological products are medical products intended for the prevention, treatment or cure of a disease condition in humans or animals; and they are also used to prevent or diagnose diseases.

Biological warfare is the use of chemical and biological agents to cause sickness or kill a defined civilian or military population during war.

Bioluminescence is simply defined as the emission of light from a biological source or living organisms.

Bioremediation is defined as the use of biological organisms including microorganisms to solve environmental problems such as contamination of the soil, land, air and water. It helps to restore polluted/contaminated soil to its unpolluted state; and thus remove all toxic wastes and chemicals that rendered the soil polluted. The biotechnological clean-up of pollutants in the environment that is microbial-based or driven.

Biostimulation is the addition of nutrients to a polluted site in order to encourage the growth of naturally-occurring chemical-degrading microbes that feed on the pollutants.

Biosurfactants are surface-active substances that are biosynthesized by living cells including animals and microorganisms. They are surfactants synthesized by microbes especially bacteria, yeasts and moulds; and thus are called microbial surfactants.

Biosurveillance is simply defined as the art of detecting disease outbreak during a bioterrorism attack or a natural epidemic occurrence in a defined human population in real-time.

Biotechnology is simply defined as the scientific manipulation of living organisms at the molecular genetics level to produce useful economic products and services that are of added-value to humanity. It is the science that puts microorganisms to work. It is any technological application   that   uses   biological   systems (including microorganisms),   living   organisms   or   their derivatives   thereof,   to make or modify products and processes for specific use.

Bioterrorism is simply defined as the unauthorized, threatened, and deliberate use of microbes (including bacteria, fungi or viruses) and their products (e.g. spores and toxins) as well as other biological and toxic substances or materials to cause death or disease in human populations, plants or animals. It is the use of microorganisms and other biological agents for aggressive or hostile purposes as against international laws regarding the usage of such agents.

Biotoxins are poisons that come from plants or animals or other living organisms.

Blister agents (vesicants) are chemicals that severely blister the eyes, respiratory tract, and skin on contact.

Blood agar haemolysis is a biochemical test that is used to determine the haemolytic ability of some pathogenic microorganisms including Streptococcus pneumoniae, Staphylococcus aureus and Micrococcus species.

Blood agents are poisons that affect the body by being absorbed into the blood.

Blooms are visible growth of planktonic or photosynthetic microorganisms especially some species of bacteria (e.g. cyanobacteria) which are produced on the body surface of water including pools, lakes and reservoirs.

Blotting is the molecular biology technique that allows molecular biologists to transfer the products of a PCR reaction (particularly nucleic acids and protein molecules) from a gel strip onto a matrix or specialized chemically reactive paper for further separation and/or studies. It is the transfer of biological samples from a gel to a membrane and their subsequent detection on the surface of the membrane.

Bottom fermenting yeast are yeast cells such as Saccharomyces carlsbergensis that is used for the production of lager beer; and which settles or flocculates at the bottom of the fermentor when the fermentation process is completed.

Botulism is a non-communicable disease and a type of food poisoning caused by the exotoxin produced by Clostridium botulinum.

Brewing is the act of producing beer. It is the process by which wort is converted into alcohol by microbes such as yeasts.

Broad spectrum drugs are antimicrobial agents that have activity against a wide variety of pathogenic microorganisms. They are active against both Gram-positive and Gram-negative bacteria.

Broth is a liquid culture media that is devoid of agar.    

Brucellosis is a genitourinary infection or disease that causes abortion in animals including pigs, cattle’s, sheep and goat. It is caused by Brucella species such as B. abortus.

Budding is a type of asexual reproduction in which the daughter cell emanates or develops from the parent cell. In budding, the daughter cell develops entirely from the mother or parent cell as a localized outgrowth.

Buffers are substances that keep a constant balance between an acid and a base or alkali in a solution.

Bursa of Fabricius is a lymphoid organ situated near the terminal end of the gut in birds or fowl (i.e. around the cloacae region) where B cells are produced.

Bursectomy is the medical procedure of removing the Bursa of Fabricius from chicken or birds.



Capsules are extracellular polysaccharide (ESP) molecules secreted by bacteria, and which are normally found outside the cell wall of the microbial cell.

Carbohydrates are macromolecules that are made up of monosaccharides as their monomeric units.

Carbon cycle is defined as the cyclical interconversion of carbon compounds in the ecosystem.

Carbonaceous biological oxygen demand (CBOD) is the amount of oxygen consumed during the oxidation of carbonaceous (carbon) compounds to carbon dioxide CO2) and other oxidized end products.

Caries is the general term used to describe the loss or decay of the dentine, root and enamel portions of the tooth caused by microbes.

Carrier is an individual who harbours a particular microbe (responsible for a given disease) but shows no clinical signs or symptoms of the disease. Carriers of a disease-causing agent are important reservoirs of some infections.

Catabolism is the cellular breakdown of complex organic molecules such as proteins into simpler and less-complex molecules utilized by the cell.

Catalase is an enzyme that breakdown hydrogen peroxide (H2O2) to water and oxygen.

Catalase test is a biochemical test that is used to identify microorganisms that produce catalase enzyme. It is used to differentiate catalase-producing organisms (e.g. Staphylococcus species) from non-catalase producing bacteria (e.g. Streptococcus species).

Caustics (acids) are chemicals that burn or corrode people’s skin, eyes, and mucus membranes (lining of the nose, mouth, throat, and lungs) on contact.

Cell culture is the laboratory technique of growing and maintaining the cells of multicellular organisms (plants and animal cells inclusive) in a favourable artificial environment conducive for growth. It is the maintenance of animal cells (inclusive of plant and human cell lines) in vitro.

Cell division is simply defined as the general way in which a microbial cell or a living organism (the parent cell in this case) reproduces itself in order to generate new offspring.

Cell immobilization is the process of fixing the cells of living organisms including plants, animals, enzymes and microbial cells in a suitable matrix capable of holding them in place.

Cell is simply defined as the basic structural and functional unit of life. It is the smallest component of all forms of life including microbial cells.

Cell theory is the scientific hypothesis that the cell is the basic unit of life found in all living organisms.

Cell wall is the rigid coating or cover of cells that is exterior to the cytoplasmic membrane, and which helps to prevent the cells from lysis by controlling the inflow and outflow of materials between the cell and its surrounding environment.

Cell-mediated immunity (CMI) is the type of specific or adaptive immunity that is mediated by T lymphocytes. They are mainly responsible for protecting the body against infectious agents that invade the host cells such as viruses and parasites or protozoa including cancer or tumour cells.

Cellulitis is an infection of the deep layers of the skin.

Central dogma describes the genetic process in which the information encoded by a gene or DNA is transcribed into messenger ribonucleic acid (mRNA) that act as a template and is further translated into specific protein molecules in the ribosome of a cell.

Centromere is defined as the point of adhesion or attachment of two chromatids in a chromosome.

Chagas disease is American trypanosomiasis that is caused by Trypanosoma cruzi.

Chemical oxygen demand (COD) is defined as a measure of the amount of chemicals (usually organic compounds) that consume dissolved oxygen in a body of water.

Chemical weapons are toxic mixtures of chemicals that cause death, temporary incapacitation, or permanent harm in a human population through their chemical actions in life processes.

Chemiluminescence is the emission of light from a non-biological source due to a chemical reaction.

Chemolithotrophic autotrophs are microorganisms that obtain their energy and electrons form the oxidation of reduced inorganic compounds such as sulphur, nitrogen and iron compounds.

Chemoorganotrophic heterotrophs are microorganisms that make use of organic compounds as their sole source of energy, carbon, electrons and hydrogen.

Chemostat is a continuous fermentation apparatus that feeds nutrient medium into the culture vessel at the same rate as the medium containing the microorganisms is removed.

Chemotherapy simply means the use of drugs to treat microbial diseases or infections.

Chemotrophs are organisms that acquire their energy or food from the oxidation of organic or inorganic compounds.

Chimera is a recombinant plasmid that contains a foreign DNA.

Chitin is the carbohydrate that makes up the exoskeletons of invertebrates such as insects.

Chloroplast is the organelle that contains the green-pigment chlorophyll, and which serve as the photosynthetic machinery of phototrophic cells and photosynthetic organisms.

Choking/lung/pulmonary agents are chemicals that cause severe irritation or swelling of the respiratory tract (lining of the nose and throat, lungs).

Cholesterol is a typical sterol found on the cell membrane of animal cells.

Chromatin is the chromosomal DNA component of a cell that is usually associated with histone proteins in a dispersed form.

Chromosome is a chromatin-like structure comprising mainly of genes or DNA associated with histone proteins; and chromosomes carries the genes of the cell. They are rod-like structures located in the nucleus of every living organism, and which are mainly made up of DNA that carries the genes or genetic information of the cell/organism. They are structures that are found in the nucleus of a cell, and that contains genes (the units of heredity) and chromatin (a nucleoprotein compound containing genomic DNA and other nucleic materials). They are found in both prokaryotic and eukaryotic cells.

Chronic diseases are long term disease that persists for a relatively lengthy period of time spanning into months and even years. Such diseases usually end in either the recovery or death of the affected host.

Citrate test is a biochemical test that is used to identify Enterobacteriaceae that utilize citrate or citric acid as their sole carbon and energy source.

Class I MHC molecules are MHC molecules that present peptide molecules from intracellular antigens (or pathogens) to T cytotoxic (TC) cells otherwise known as CD8+ cells. They are found on the surface of virtually all nucleated cells of the human body.

Class II MHC molecules are set of MHC molecules that present peptide molecules from antigens or pathogens to T helper (TH) cells also known as CD4+ cells. They are mainly found on the surfaces of immunocompetent cells especially antigen presenting cells (e.g. macrophages, langerhans cells, B cells and dendritic cells).

Class III MHC molecules are a group of free unrelated protein molecules which unlike class I and class II MHC molecules do not take part in the presentation of peptide molecules from antigens to T cells.

Clonal dissemination of microbes refers to the spread of specific clones of an organism throughout a particular community.

Clonal expansion is the enlargement in the number of competent B cells or T cells with the same antigenic specificity as the progenitor (parent) B cell or T cell. It is the proliferation of B cells into more B lymphocytes for the production of antibody-producing plasma cells and memory B cells.

Clones are population of identical cells or DNA molecules.

Cloning is a molecular biology technique which is used to make millions of copies of a particular gene of interest or a piece of DNA molecule. It generally involves taking a piece of DNA molecule (containing specific gene sequence of interest) from a donor organism where it naturally exists and putting same into a cloning host cell (e.g. Escherichia coli) through the help of a vehicle such as a vector which carries the gene of interest into the recipient host.

Cloning vectors therefore are DNA molecules that are used to transport cloned sequences of a gene or DNA between biological hosts and the test tubes.

Clue cells are vaginal epithelial cells covered with bacteria cells. These cells are found in patients suffering from bacterial vaginosis (caused by Gardnerella vaginalis).

Cluster of Differentiation (CD) represent cell surface molecules or markers used in defining leukocytes especially the T cells based on an internationally recognized system of classification.

Coagulase is an enzyme that causes blood plasma to clot, and it is produced by pathogenic bacteria as part of their virulence factor. It is a blood-coagulating enzyme produced by some pathogenic bacteria (e.g. Staphylococci).

Coagulase test is a biochemical test that is used to distinguish pathogenic Staphylococcus aureus (which is coagulase positive) from nonpathogenic strains of S. aureus (which is coagulase negative).

Coding region of a gene is the part of the gene that specifies the protein to be made. It is the DNA sequence of the gene.

Codon is a group of three successive nucleotides found in the mRNA; and they base-pair with the anticodon of an individual tRNA that carries a specific amino acid molecule. It is a sequence of three bases in mRNA (messenger ribonucleic acid) that encodes a specific amino acid. Codons are sequences of three (3) bases in an mRNA that encodes specific amino acids.

Coenocytic hyphae are hyphae without cross-walls. They contain more than one nucleus (i.e. they are multi-nucleated).

Cofactors are the non-protein components of enzymes that take part in the catalytic functions of enzymes.

Coliforms (coliform bacteria) are bacteria that serve as indicators of feacal contamination of samples including water, milk and food. They are not themselves pathogenic but they are occupants of the digestive systems of humans and animals; and their presence in the human digestive system makes them to be abundant in human feacal matter.

Collagenase is an enzyme produced by bacteria and which hydrolyzes collagen (a protein found in fibrous connective tissues such as muscles and bones), thereby allowing the organism C to spread in the tissues and cause sepsis. It is mainly produced by Clostridium perfringens (the causative agent of gas gangrene).

Colonial morphology is the size, shape, colour, texture and the general structure of an individual colony of a particular microorganism (bacterium or fungus) on a culture media plate that supports its growth.

Colonization is the process in the pathogenicity of an organism in which the pathogen establishes or inhabits the internal or external body surface in order to cause infection.

Colony forming unit (CFU) is the microbiological expression of the number of bacteria or fungi in a microbial population (which is usually seen as distinct colonies on solid agar plates). It gives a measure of the viable cells (bacteria and fungi inclusive) present in a culture.

Colony is a macroscopically visible population of cells growing on solid media, and that arises from a single cell.

Colorimeter is a device used to test the concentration of a solution by measuring its absorbance of a specific wavelength of light.

Colorimetry is the technology that is used to quantify and describe physically the human perception of colour.

Colostrum is the first secretion of the mammary gland (breast) produced before proper lactation commences in a nursing mother.

Columella are axial or central, unicellular or multicellular structures formed within the fruiting body of some fungi. It is an extension of the sporangiophore into the cavity of the sporangium.

Commensalism is an association in which one organism (known as the commensal organism) benefits from the relationship but the other organism neither benefit nor surfer from the alliance.

Communicable diseases are infectious diseases that are contagious. They are infections that can be transferred or passed on from one person (sick person) to another individual (susceptible host).

Competition is defined as a microbial interaction between two microbes that are attempting to use the same resources in a given habitat. It arises when two organisms living in a particular population tries to acquire the same resources or nutrients especially those resources that are in short supply in their community.

Complementarity is the ability of single-stranded DNA molecule to base-pair or anneal again after being denatured.

Complements are a series of serum proteins that play significant role in innate defense mechanism by catalyzing the killing of bacterial cells and also facilitating the migration of white blood cells to sites of inflammation or infection in the body.

Compost is simply defined as an organic matter comprising of plant, human or animal waste that have been decomposed and recycled or reused as a fertilizer to improve the fertility of the soil.

Composting is the controlled aerobic decomposition of organic matter by the action of microorganisms in the soil.

Conditioning is the next stage after the primary fermentation process in beer production – where the green beer is allowed for some time to age in order to improve in taste and quality. It is also known as ageing.

Confounding factors (variables) are confusing factors in arise in an epidemiological study and, which are directly or indirectly related tone or more of the variables already define in the study.

Conidia are the asexual reproductive spores of fungi.

Conjugation (mating) is the form of gene transfer and recombination in bacteria through which genetic materials are transferred from one bacterium to another through a direct cell – to – cell contact.

Contact tracing is defined as an epidemiological tool used by epidemiologists and public health personnel’s to trace and find every person who may have directly or indirectly come in contact with an individual infected with a highly infectious disease.

Continuous cells are cell lines that are capable of more prolonged and indefinite growth. They are immortalized cell lines that can be passaged or subcultured several times.

Continuous culture is the cultivation of microorganisms in a culture or growth medium in such a way that the growth of the organism is maintained at an exponential level. It is an open system of culture, and continuous culture involves the continual supply of growth nutrient too the culture system as the available nutrients are being depleted by the growing organism.

Continuous fermentation is defined as the fermentation process in which sterile growth nutrients are added continuously to the fermentation vessel and an equal amount of converted nutrient solution (end-product) with microorganisms is simultaneously harvested in the process. It is also known as an open culture system.

Convalescent carrier is an individual who have just recovered from a particular disease but who still carry large amounts of the pathogen responsible for the infection.

Convalescent period of disease is referred to as the recuperative period is the period of recovery from a particular infection in which a previously ill patient regains his or her normal body functions and returns back to normal life free of the disease. The convalescent period which can also be referred to as recuperative period is the period of recovery from a particular infection in which a previously ill patient regains his or her normal body functions and returns back to normal life free of the disease.

Cooperation is a type of symbiosis that benefits both organisms in the relationship.

Cross linking is another immobilization technique in which microbial cells can be immobilized by cross-linking them with each other using certain chemicals or reagents with bi- or multifunctional reagents such as glutaraldehyde.

Cross-reactivity is the capacity of a given immunoglobulin molecule or T cell receptor (TCR) to react with multiple antigens that share common antigenic determinants or epitopes.

Culture in microbiology refers to colonies of microorganisms (for example bacteria) that grow and multiplies in or on a culture medium. It is generally the microbiological laboratory technique in which the growth of microorganisms in a growth medium (solid, liquid or broth) is enhanced for visibility and easy study.

Culture media are nutrient medium or preparations that supports and allow microorganisms to be propagated in the laboratory for further study.

Culturing technique is used for the propagation of microorganisms in the microbiology laboratory; and it is an important procedure required for studying the morphological characteristics of microbes especially on solid culture media.

Cutaneous anthrax is an ulcerative sore on the skin and the type of anthrax that affects the outer skin.

Cutaneous mycoses are fungal infections of the skin, nails and hairs; and they are mainly caused by dermatophytes.

Cyclosporiasis is a persistent diarrheal parasitic disease that is acquired through the consumption of food and water contaminated with feaces of man and other animals containing the oocysts of the parasite, Cyclospora cayetanensis.

Cystitis is the infection of the urinary bladder.

Cytochrome-c oxidase is a respiratory enzyme is an important enzyme of the electron transport chain (ETC), where it catalyzes the transport of electrons from a donor compound (e.g. NADH) to oxygen, the final electron acceptor.

Cytokines are low-molecular weight molecules of the innate immune system which are released by leukocytes to help in the regulation of inflammatory response during microbial invasion.

Cytopathic effects are observable morphological changes that occur in cells because of viral replication. It encompasses those biochemical and/or morphological changes that occur in viral infected cells, and which indicate viral infectivity and replication in a particular host cell.

Cytotoxicity is the cellular damage of metabolic pathways, structures and intracellular processes of a living organism which ultimately result in the loss of function or impaired metabolic function.

Cytotoxins are toxins found in the general tissues of the body where they cause a series of local and systemic damages (e.g. in the pathogenicity of Staphylococcus aureus).



Decline period of an infection is the phase of fast or slow reduction in the signs and symptoms of a disease, and which allows the sick individual to regain his or her normal wellbeing.

Decline phase which can also be called the death phase is the stage in the growth of microorganisms in which the number of viable microbes in the growth medium continues to decrease. And it occurs when nutrient depletion takes place in the growth vessel.

Dematiaceous fungi are fungal organisms with cell walls that contain the skin pigment, melanin.

Denaturation is the first stage in a PCR reaction, and it is the stage at which a double stranded (ds) DNA molecule is unwounded or separated into their individual complementary single strands. At this stage, the PCR reaction mixture is heated to a high temperature (about 94-98oC) for 20-30 seconds.

Dendritic cells (DC) are special type of leukocytes found in the skin, thymus, spleen and lymph nodes, and which primarily act as professional antigen presenting cells. They are motile and non-phagocytic adherent cells that contain numerous mitochondria and nucleus. They are cells of the immune system that mainly act as antigen presenting cells (APCs); and they comprises of langerhans cells found underneath the skin.

Denitrification is the process of reducing nitrate and nitrite into gaseous nitrogen (N2).

Dental caries is simply defined as the decaying of the teeth. It can also be called dental decay; and it is a gradual disintegration of the teeth beginning from the tooth surface and progressing inwards. The loss of the tooth enamel is also known as dental enamel. It is the destruction of the enamel of the teeth due to bacterial activities. It is usually initiated by direct demineralization of the enamel of teeth due to lactic acid and other organic acids which accumulate in dental plaque as a result of microbial activities.

Dental plaque is simply the materials that adhere to the teeth; and these materials that adhere tightly to the teeth of animals especially humans consists of several substances and microbes inclusive of bacterial cells, food particles, fungal cells, salivary polymers, and the extracellular products of microorganisms that habitually inhabit the oral cavity. It is defined as the tenacious microbial deposit that forms on the hard tissue of the tooth surface. It comprises of living, dead and dying bacteria and their metabolic products as well as the components from the host saliva.

Dentinal caries is the loss of the dentine.

Deoxyribonucleic acid is the genetic material of the cell which directs cell division or replication in a cell.

Dermatophytes are fungal cells that cause skin infections or diseases. They are a group of fungal organisms that can degrade the keratin layers or tissues of animals and humans.

Deuteromycetes are generally known as “imperfect fungi” unlike the ascomycetes, zygomycetes and basidiomycetes which are “true fungi” because they have a sexual cycle of reproduction.

Differential media or indicator media are growth media that allow certain bacteria to have distinct colonies on the culture media especially members of the Enterobacteriaceae family.

Diffusion is the transportation of solute molecules from a region of higher concentration to a region of lower concentration.

Diluents are essential substances in the microbiology laboratory because they help in the dilution of a highly concentrated solution in order to get a workable concentration for a given task.

Dilution is the laboratory technique of reducing the original concentration of a sample or solution either by half or to a more practical concentration. It involves a reduction in the concentration of the original solution.

Dimethyl sulphoxide (DMSO) is a non-ionized polar solvent that solubilizes both lipophilic and hydrophilic substances. It is also used as a cryoprotectant in most freeze-drying procedures to freeze cells in the laboratory.

Dimorphism is the term used to describe a fungus with two growth forms i.e. the yeast and mould forms. And such fungi are called dimorphic or diphasic fungi. Examples of dimorphic fungi include Histoplasma capsulatum, Blastomyces dermatitidis, Paracoccidioides species, Candida albicans and Sporothrix species.

Diploid cells are cells that have two sets or copies of chromosomes. They are cells that contain a full set of the Plasmodium parasite chromosomes.

Direct observed therapy is anti-tuberculosis program where TB patients are regularly monitored to ensure that they take the full course of their medication so that drug resistance does not develop and the public health is protected. In direct observed therapy (DOT), TB patients visit the health center, clinic or hospital for their medication.

Direct plate counting is a microbiological technique that is used to evaluate the actual bacterial content of a product or specimen; and they give an estimate of viable or living cells present in a sample.

Disaccharides are carbohydrates or sugars that consist of two monosaccharides held together by glycosidic bond.

Disinfectant is an antimicrobial agent that disinfects (i.e. removes or destroys microorganisms), and it is only used on non-living objects such as hospital equipments, floors, sinks, walls, desks, laboratory bench and at home to disinfect surfaces and objects likely to harbour microbes.

DNA gyrase is an enzyme that introduces negative supercoils into newly synthesized DNA molecules.

DNA ligase is a stitching enzyme that joins DNA fragments together during DNA replication. it is an enzyme that specifically joins cut (nicked) DNA molecules together. They repair and join two individual single-stranded DNA fragments (i.e. the cloning vector and the DNA molecule to be cloned) cut by the same restriction endonuclease.

DNA microarray is simply a high-throughput molecular biology technique that is used to determine how genes work at any given point in time in a cell i.e. how genes are turned off or on in a cell.

DNA polymerase are specialized enzymes with a variety of biological functions during DNA synthesis such as the synthesis of new DNA strands, proof-reading of gene sequence in the newly synthesized DNA strand, repairing and filling of gaps formed on the lagging strand during DNA replication, and the extension of DNA strands.

DNA polymerase I is an enzyme that synthesizes DNA molecules complementary to a DNA template in the 5′-3′ direction. It generally synthesizes DNA on a DNA or RNA template.

DNA template is the macromolecule that contains the DNA region or gene sequence to be copied and amplified.

DNase enzyme is a nuclease enzyme which digests DNA.

Doubling time is the time it takes a bacterial population to double and increase its population size. It is the time required for a microbial population to double.

Droplet infections are diseases or infections transmitted via the respiratory tract.

Drug interaction is defined as the biological phenomenon in which the antimicrobial activity of a particular drug is influenced or affected by other substances (e.g. food, drinks or herb) or another medication.

Dysuria is the pain experienced on passing urine.



Ectoparasites are parasites that live on the body of their host. Example of ectoparasites include: lice and tick.

Effector cells of the immune system are immunologically responsive cells that directly encounter antigens and facilitate their neutralization and possible elimination from the host. Examples of effector cells include plasma cells and T cells. They are immune system cells such as antibodies that specifically respond and eliminate antigens that invaded a host’s body.

Efflux pumps are pumps found in bacteria cells; and they help the organism to export antimicrobial agents and/or antibiotics and other chemical compounds out of the bacterial cell.

Egg candling is defined as a technique that is used to determine the condition of the air cell, yolk, and white component of an embryonated egg prior to its usage for viral culture.

Electron acceptors are molecules that accept electrons in the course of an oxidation-reduction (redox) reaction. They can also be called oxidizing agents.

Electron donors are those molecules that donate electrons in a redox reaction. They can also be called reducing agents.

Electron transport chain is a system that comprises of a sequence of electron carriers which work cooperatively to transfer electrons from electron donors to electron acceptors within the cell of a living organism. It shows a series of oxidation-reduction (redox) reactions in which electrons in the form of energy or ATP can be translocated within the cell or from one part of the cell to another as electrons flow within the energized membrane.

Electrophoresis refers to the movement of a solid particle (e.g. nucleic acids) through a polymer matrix or gel under the influence of electric field. It is a molecular biology technique that is used to separate nucleic acid molecules and other macromolecules mainly on the basis of their charge to mass ratio as they migrate through a gel in an electric field.

Electroporation is the in vitro molecular biology technique that is used to increase the efficiency of transforming a bacterial cell. It is a physical method of transforming bacterial cells using electric charges or pulses.

Emerging diseases are new infectious diseases caused by novel pathogenic microorganisms that are still evolving within a particular population. They are generally the first outbreak of an infectious disease caused by unknown pathogenic microorganisms; and they also include infectious diseases that are known but whose incidence in a defined human population have significantly increased in frequency in the past twenty years.

Endemic diseases are infectious diseases that are constantly present at very low frequency in a particular population. Such a disease affects only relatively low members (or few persons) of the population at a given time period.

Endergonic reactions are chemical reactions that require an input of energy for the reaction to occur or progress.

Endocytosis is simply defined as the process in which a virus is taken intact into a host cell.

Endogenous antigens are naturally occurring antigenic substances found within an animal and which are unique to every individual.

Endogenous fungal infections are fungal infections caused by fungi that are members of the human normal microflora.

Endogenous pyrogens are neither endotoxins nor lipopolysaccharide (LPS), but they are fever-inducing agents that arise in the body of a host when exogenous pyrogens come in contact with certain host cell molecules such as monocytes or macrophages. They originate outside the body and induce temperature elevations when injected into humans and animals.

Endoparasites are parasites that live inside the body of their host. Example of endoparasites include: worms, Plasmodium and Trypanosome.

Endophytes are microorganisms that live within the tissue of a plant as endosymbionts, without causing symptoms of a disease or any apparent disease. They are extremely common and highly diverse microorganisms that live within plant tissues, but usually remain asymptomatic in nature.

Endospores are the heat-resistant forms of bacteria.

Endosymbionts are organisms that live inside other living organisms.

Endosymbiosis is the association or relationship formed by endosymbionts.

Endotoxins are cell-associated toxins, and they are released by a dead bacterial cell. They are lipopolysaccharides (LPS), and are located on the outer membrane of Gram negative bacteria. Exotoxins are produced by a living bacterial cell, and they are usually proteins that act enzymatically. They are protein molecules excreted by growing bacteria into the surrounding medium where the bacterium grows or into the tissues, cells and circulatory system of their human host.

Enriched media are solid culture media that also contain additional growth nutrients (e.g. blood) like enrichment media for the cultivation and isolation of fastidious bacteria.

Enrichment media are liquid culture media or broth that supports the growth of a particular bacterium while inhibiting the growth of unwanted bacteria.

Enterobiasis is a parasitic roundworm infection caused by intestinal nematodes such as Enterobius vermicularis (also known as threadworm or pinworm).

Enterohaemorrhagic Escherichia coli are pathogenic strains of E. coli that are the causative agents of haemorrhagic colitis (a life-threatening bloody diarrhea), and they mainly affect the colon (large intestine).

Enteroinvasive Escherichia coli are pathogenic strains of E. coli that cause E. coli-associated dysentery that resembles shigellosis (caused by Shigella dysenteriae).

Enteropathogenic Escherichia coli are pathogenic strains of E. coli that causes diarrhea in infants and children in developing countries.

Enterotoxigenic Escherichia coli are pathogenic strains of E. coli that are the main causative agents of traveler’s diarrhea in people visiting developing countries.

Enterotoxins are toxins produced extracellularly by microbes as they grow; and these toxins are unique in the sense that they produce immediate damage to the small intestine of the host especially in cases where microbial infected food is consumed. They are toxins found in the intestinal mucosa where they cause a series of gastrointestinal infections (e.g. in the pathogenesis of Vibrio cholerae).

Entner-Doudoroff pathway is a metabolic pathway that is used for the generation of pyruvate in organisms that lack glycolytic pathway.

Entrapment is the immobilization technique in which microbial cells are entrapped in a support matrix or inside fiber materials where they are held in place.

Entropy is defined as a measure of the disorderliness or randomness of a system.

Enveloped viruses are viruses that have envelopes.

Envelopes are the lipid-containing outer membranous layer that surrounds the nucleocapsid in some viruses.

Environmental microbiology is the study of microbial processes in the environment, microbial communities and microbial interactions with other living organisms in the environment. It is the branch of microbiology that studies the role of microorganisms in the maintenance of a healthy, quality, and sustainable environment. It is the branch of microbiology that studies the role of microorganisms in the maintenance of a healthy, quality, and sustainable environment.

Enzyme linked immunosorbent assay (ELISA) is an immunoassay or serological test that is used for the quantification or identification of specific antibodies or antigens in biological specimens (e.g. serum or blood). ELISA is mainly based on the principle of enzyme-substrate reaction.

Enzymes are protein substances produced by living organisms and which catalyze or speed up the rate of chemical reactions in them.

Eosinophils are polymorphonuclear (PMN) granulocytes with phagocytic action and cell-surface-receptor-sites for the attachment of antibodies especially IgE and IgG. They are a type of granulocytes that can easily be stained with eosin, a red-crystalline dye.

Epidemic diseases are infectious diseases that increase rapidly in frequency above the tolerable or predictable level in a particular population over a given period of time. It is a disease that affects a reasonable high number of people in a community at a given time.

Epidemiology is defined as the field of medical science that studies the occurrence, distribution, and determinants of disease and health-related issues, and the application of same in the control and prevention of an infectious process and a pathologic state in a defined human community/population.

Epitope is the discrete site on the structure of an immunogen that is recognized by an antibody. It is those areas on the surface of an immunogen that stimulate specific immune response in a host.

Ergosterol is the sterol found on the cell membrane of fungi.

Ergot is the dried sclerotium of Claviceps purpurea.

Ergotism is a psychotic and neurological disease caused by Claviceps purpurea in humans and animals who eat crop plants infested by the fungus Claviceps purpurea. It is the toxic condition or disease that is caused by the consumption of grains infected with ergot or ascomycete.

Ethics are the principles of right and wrong that are acceptable to a group of people or an individual. It is a system of standards that governs the morality and acceptability of any medical research involving human or animal subjects.

Eukaryotic cells are organisms or cells that have a membrane-bound nucleus. They are distinct group of organisms that have a unit membrane-enclosed nucleus and other organelles such as the mitochondria that are membrane-bound.

Eutrophication is defined as the enrichment of a habitat or environment with inorganic materials including phosphorus and nitrogen that support and encourage the growth of plants and algae in the affected environment.

Ex vivo delivery is the gene therapy technique in which cells extracted from a patient are genetically engineered in vitro and then re-introduced into the host’s body.

Excipients are substances added to drugs during their production in order to make them into pills (i.e. as capsules or tablets). They are substances added to drug or vaccine in order to make into an actual pill for administration.

Exergonic reactions are chemical reactions that occur without the input of external energy; and such reactions generally lead to the production of energy.

Exfoliatin are protein toxins produced by Staphylococcus aureus strains that cause staphylococcal scalded skin syndrome (SSSS) in humans. Exfoliatin can also be called exfoliative toxins (ET).

Exogenous antigens are foreign molecules or substances that are external to the body of a host.

Exogenous fungal infections are fungal infections acquired externally from the environment via the inhalation of fungal spores in aerosols or dust particles.

Exogenous pyrogens are endotoxins or lipopolysaccharides (LPS) of Gram negative bacteria that induce fever in animal or human host when administered intravenously. They are pyrogens generated by the host body; and they have potent inflammatory and pyrogenic effects in the body.

Explant is simply defined as a fragment of tissue that is transplanted from its original (parental) host organism and maintained in an artificial growth medium in vitro.

Explantation is defined as the process of removing cells or tissues from their normal in vivo environment (i.e. from their parental host organism) and maintaining their growth in vitro in an artificial growth environment.

Extended spectrum beta-lactamases (ESBLs) are beta-lactamase enzymes that breakdown or hydrolyze broad-spectrum beta-lactam drugs especially the third-generation oxyimino-cephalosporins (e.g. ceftazidime, ceftriaxone and cefotaxime).

Extensively drug-resistant tuberculosis is a tuberculosis infection caused by Mycobacterium tuberculosis strains that are resistant to the two best first-line TB treatment drugs (isoniazid and rifampin), plus any fluoroquinolone and at least one of the three injectable second-line TB drugs (amikacin, kanamycin, or capreomycin).

Extrinsic factors are external factors that influence the growth of microorganisms in food. They include environmental factors such as temperature that encourage the growth of microbes in food.

Extrinsic factors of food spoilage are the non-substrate factors that affect the spoilage of foods and food products and which are not innately found in the foods. They include temperature, relative humidity, gases and the amount or number and type of microorganisms present in the food.



Facultative bacteria are bacteria that grow in the presence and absence of oxygen.

Fastidious bacteria are bacteria that require additional growth nutrients such as blood or serum for growth.

Fed-batch fermentation is defined as the liquid fermentation process in which growth nutrients are periodically added in the fermentation medium during fermentation.

Fermentation is a microbiological process in which microorganism’s breakdown energy-carrying compounds or substrates under aerobic or anaerobic condition to produce economically useful products. It occurs when microorganisms of industrial importance breakdown susceptible substrate molecules as part of their own metabolic processes. Fermentation is the chemical transformation of organic substances into simpler compounds by the action of enzymes, complex organic catalysts, which are produced by microorganisms such as molds, yeasts, actinomycetes or bacteria. It is the energy-yielding type of metabolism in which an energy-substrate is oxidized or metabolized to release free energy in the absence of an external electron acceptor (e.g. oxygen).

Fermentation media is simply defined as those preparations that support the growth of microorganisms used in a fermentation process.

Filtration is a sterilization technique that removes suspended microbial particles and/or cells from liquids or solutions by passing them through special types of permeable membranes generally known as membrane filters. It is the separation of particles from fluid or liquids by the use of a porous material that allows the passage of the fluid but stops or holdback unwanted particles from passing through it.

Fimbria  are hair-like structures which are uniformly found on the outside of a prokaryotic cell.

Flagella are long whip-like structures that extend from the body of certain cells or organisms. They are organs of motility, and thus help to propel microorganisms (eukaryotic and prokaryotic) from one point to another.

Flow cytometry is the high-throughput technique that is used in molecular biology to analyze the chemical and physical properties of samples (especially fluids) when they pass through a laser light.

Fluid pumps are structures through which nutrients are introduced into the fermentor.

Fluxomics is the measurement and determination of fluxes or changes in the metabolic pathways of the cell.

Fomites are inanimate or non-living objects that can help to transmit infectious disease agents or infections from one person to another and from one location to another. They include water, tables, chairs and food that help to transmit infectious agents and/or diseases to susceptible human or animal hosts.

Food borne diseases are diseases caused by the ingestion of food borne pathogens. They are generally regarded as gastrointestinal infections that occur when microbes are ingested via contaminated foods or food products.

Food intoxicating organisms are microbes that cause food intoxication.

Food intoxication is the food borne infection that has to do with the ingestion of preformed toxins of microbes in food.

Food microbiology is the branch of microbiology that deals with methods for keeping microorganisms (especially food-borne pathogens and spoilage microbes) from growing in food during handling, processing and storage. It is the area of microbiology that studies the interactions of microorganisms and food; how this association can be exploited to produce or process food; and how microbes cause food spoilage.

Food poisoning is defined as the microbial infection or disease that is caused by the ingestion of food/food products that contains pathogenic microorganisms.

Food poisoning organisms are food borne pathogens that must grow in food in large numbers and cause infection when consumed together with the food.

Food preservation is the technique used to prevent food spoilage. It encompass all the methods employed to inhibit or delay the growth of microorganisms especially food spoilage microbes in food and/or food products.

Food spoilage is simply defined as the change in the overall appearance, taste and smell of a particular food or food products due to microbial activities.   It is the change in the taste, smell and appearance of food or food products due to microbial activities caused especially by fungi and bacteria.

Frame shift mutation is a type of mutation that occurs within the protein coding region of a gene.

Fungi are eukaryotic and heterotrophic microorganisms that do not contain chlorophyll but obtains its nutrient through the absorption of food and/or nutrients in its environment.

Fungicidal agents are those antifungal agents that kill fungi.

Fungimia is the presence of pathogenic fungi in blood.

Fungistatic agents are antimicrobial agents that inhibit or stop the growth of fungi.



Gametangia are gamete producing structures of fungi.

Gametes are the reproductive elements of living organisms that includes the male and female sex cells.

Gametocytes are the precursors of the sexual forms of Plasmodium parasite, which are released as either male or female gametes within the gut or stomach of the mosquito.

Gamma haemolysis is a type of haemolysis that produces no clear-cut lysis of RBCs.

Gastrointestinal anthrax is the anthrax that affects the gastrointestinal tract (GIT)

Gel electrophoresis technique is a molecular biology technique that is used to separate nucleic acid molecules (DNA and RNA) according to their sizes and conformation or charges. It is generally used in the molecular biology laboratory for the separation and purification of nucleic acid fragments.

Gene expression is the process of turning the information from the gene in the DNA into a protein molecule or other molecules that it encodes.

Gene is a sequence of nucleotides in the nucleic acid molecule (DNA and RNA inclusive) of an organism which encodes the synthesis of unique protein molecules with specific biological function.

Gene reassortment is defined as the reassortment or rearrangement of the genetic makeup of an organism.

Gene therapy is defined as the specific genetic manipulation and modification of an organism’s genome or genes through the delivery of therapeutic DNA or genes into host cells with little or no toxicity as a way of treating an inherited genetic disease or correcting a disorderly gene.

General purpose media or basic medium are routine culture media that are used for the cultivation of microorganisms in the microbiology laboratory.

Genes are the chemical blueprints that determine an organism’s phenotype; and when the DNA or genes of one particular organism is moved to another organism, the genetic traits or genotype of the former organism will be transferred to the recipient organism. They are sections of the deoxyribonucleic acid (DNA) that codes for the synthesis of a specific protein sequence in a cell.

Genes are the hereditary unit or genetic material that is transmitted from parents to their offspring’s and from one generation to another; and they are known to reside within the DNA of every living organism.

Genetic disorder is a disease that is caused by a mutation (i.e. a change) in the gene of an organism; and such molecular diseases can be passed on from parents to their offspring’s who inherit the defective gene.

Genetic engineering is defined as the process of manipulating the genetic makeup of an organism. It is the modification of an organism’s genetic composition by artificial means.

Genetically modified crops are crops whose DNA have been genetically engineered to produce different varieties of qualities.

Genetically modified foods are foods that are genetically engineered foods or food products produced from organisms whose genetic materials have undergone genetic manipulation in the laboratory.

Genetically modified organisms (GMOs) are organisms whose nucleic acid (particularly DNA) has been genetically engineered or altered. They are those plants, animals or microorganisms whose genetic makeup or DNA has been changed through genetic engineering.

Genetics is simply defined as the study of genes and hereditary.

Genome is the entire set of genes found in an organism.

Genomic DNA is a double helix structure that is composed of several components including purines (adenine and guanine) and pyrimidines (cytosine and thymine) as  nitrogenous bases, deoxyribose sugar (a pentose sugar) and phosphate groups.

Genomics is the sequencing and analysis of the genetic make-up of an organism.

Genotype is simply defined as the total genetic makeup of an organism. It generally refers to the entire gene that encodes the characteristics of an individual organism.

Genus contains one or more species of organism that is different and entirely separate from species of other genera.

Geochemical microbiology is the branch of microbiology that studies the applications of microorganisms in the mining of metals, crude oil and other natural resources from their natural sources or the ground.

Geomicrobiology is the study of the interactions between microbes and minerals. It is the branch of microbiology that studies the applications of microorganisms in the mining of metals, crude oil and other natural resources from their natural sources or the ground.

Geophilic fungi are dermatophytes that reside naturally in the soil. Example is Microsporum gypseum.

Geographical information system (GIS) is a data-based management system that organizes and displays digital map images from remote sensing in order to analyze the relationships between mapped features from the mapping.

Germ line gene therapy is the gene therapy technique that targets the germ cells.

Germ theory is the theory that human infectious diseases are caused by specific variety of pathogenic microorganisms including but not limited to bacteria, fungi, protozoa and viruses.

Gingivitis is a type of periodontal disease that affects the supporting structures of the teeth such as the enamel, periodontal membrane and the alveolar bone. It is a dental disease or infection (gingival disease) that is confined to the gum and has little or no influence on the teeth itself.

Gingivitis is simply defined as the inflammation of the gum (gingivae) caused by microbial activity. It is the redness and swelling of the gingival tissues or gum as a result of bacterial infection.

Global warming is the term used to describe the unusual increase in average global temperatures of the earth’s climate due to the greenhouse effect. The term global warming is often used interchangeably with the term climate change.

Gluconeogenesis the metabolic process of maintaining the blood glucose levels of living systems (especially when they are depleted) by making glucose from pyruvate. It is the biosynthesis of glucose from pyruvate when the blood glucose level is low.

Glycogen is the form in which carbohydrate is stored in animals.

Glycolysis is the metabolic pathway by which glucose is oxidized or broken down to pyruvate. It is the pathway that carries out glucose degradation in living systems including microbes in order to release energy meant for cellular and metabolic work in the cell.

Golgi apparatus is the site for transfer, storage and packaging of macromolecules from endoplasmic reticulum for secretion to other organelles of the cell.

Good manufacturing practice (GMP) is defined as those general rules that govern the manufacture and/or production of a safe, efficacious and microbial-free pharmaceutical product. It is simply defined as those general rules that govern the manufacture and/or production of a safe, efficacious and microbial-free pharmaceutical product.

Graft versus host disease (GVHD) is a medical condition or reaction that develops when cells from the grafted tissue or organs (i.e. from the donor host) react against or with the recipient’s own tissues leading to an immunological response that facilitates the rejection of the transplanted tissue/organ. GVHD is a type IV hypersensitivity reaction.

Gram staining technique is a differential staining technique that is used to diffenetiate Gram positive bacteria (which stains purple) from Gram negative bacteria (which stains red or pink) in the microbiology laboratory; and this differentiation is mainly based on the cell wall components of bacteria.

Granulocytes are a type of white blood cells (WBCs) or leukocytes that contain granules in their cytoplasm.

GRAS simply means Generally Regarded As Safe; and the acronym is used to describe those microbes including bacteria, fungi and actinomycetes that are naturally non-pathogenic and can be used for the production of products consumed for either health benefits or as foods. The end-product of organisms referred to as GRAS is usually free from toxic substances.

Greenhouse gases are those gases, such as water vapor, carbon dioxide, ozone, nitrous oxide, and methane, which allow solar radiation to pass through to the earth, but block outgoing long wave radiation. The effect of these gases in keeping the earth’s climate warmer than normal is generally described as greenhouse effect.

Growth factors are growth precursors or nutrient constituents which microorganisms (e.g. bacteria) cannot synthesize on their own but must be obtained from their immediate environment.

Growth is an irreversible increase in the size of an organism. It is one of the characteristics of living organisms.



Haematopoiesis is simply defined as the biological process involved in the formation of blood cells (i.e. white blood cells, red blood cells and platelets) and other cellular components of blood particularly the immune system cells such as the B and T cells in the bone marrow.

Haematuria is the presence of blood in urine.

Haemoglobin is a protein that is found in the red blood cells (RBCs); and its main function is to transport oxygen from the lungs to the body tissues.

Haemolysins are exotoxins which react as antibodies homologous to the surface antigens of red blood cells (erythrocytes).

Haemolysis is the breakdown of red blood cells (RBCs). It is carried out by certain bacterial species including Streptococcus and Staphylococcus species that produce extracellular enzymes which facilitate the lysis or breakdown of the red blood cell component of whole blood.

Haemolytic disease of the newborn (HDN) is a Type II hypersensitivity reaction in which the maternal antibodies (specifically IgG) produced against fetal Rhesus (Rh) antigens or RBCs crosses the placenta to cause haemolysis in the neonate (i.e. the destruction of fetal RBCs). It is also known as erythroblastosis fetalis.

Halitophobia is the fear of bad breath.

Halitosis is an oral health condition that affects the oral hygiene of humans, and it is mostly experienced as mouth odor. Halitosis can also be called bad breath.

Halophiles are microorganisms that require high sodium chloride concentration for growth or can thrive in environments with high salinity. They are archaea organisms that live in habitats with high salt concentration.

Halotolerant microorganisms are those organisms that can tolerate or survive in environments with very low aw levels.

Haploid cells are cells that contain a half set of the entire Plasmodium parasite chromosomes.

Hazard analysis and critical control point is an internationally recognized food safety system that is employed in the production line of food and food products in food processing industries to ensure food safety, food hygiene and good food quality. It is a quality assurance technique or system that is used especially in food processing and production industries to evaluate the possible hazards or risks that are eminent in the entire manufacturing process of food and food products so that sustainable measures could be put in place to contain and minimize them.

Health determinants are those fundamental or primary environmental factors including social, cultural, religious and economic factors that are directly or indirectly responsible for the evolving of disease or better health of a people.

Health indicators are variables or factors that can be measured directly by public health workers and other health policy makers in order to establish the exact state of health of members of a given population/community. Typical examples of such indicators include life expectancy, education, and economic development which can be used to determine the Human Development Index (HDI) of a people or nation.

Healthy carrier is a person who harbours a pathogen but is not sick or showing any clinical signs or symptoms associated with the disease caused by the agent.

Heat-fixing is defined as the microbiological technique of attaching bacterial cells onto the surface of a glass slide by the use of a Bunsen burner flame or 70 % of methanol.

Helicase is the enzyme that unwinds double stranded DNA molecule prior to DNA replication. They are primarily responsible for the separation or unwinding of the double stranded circular DNA molecule of microbial cells.

Hemadsorption is the phenomenon that occur when red blood cells (RBCs) added to a cell culture plate during the incubation of the plate gets attached to the plasma membrane of the infected cultured cells which have been altered by the cultivated virus. It is the adsorption of red blood cells (erythrocytes) to the surface of virus-infected host cells.

Herd immunity is a group resistance of a population against a particular disease and the spread of its disease-causing agent in the same population. It is a collective type of immunity that is demonstrated by a community against a particular pathogen and disease within the same environment.

Heredity is defined as the process in which genetic material (particularly DNA) is transferred from parents to their offspring’s.

Heterofermenters are lactic acid bacteria that carryout heterolactic fermentation.

Heterolactic fermentation is a type of lactic acid fermentation in which sugars such as lactose or glucose are fermented or converted to a range of end-products. In this type of fermentation, more than one end-product is produced.

Heterotrophs are organisms (e.g. fungi, animals and protozoa) that depend directly or indirectly on the autotrophs for food because they cannot manufacture their own food. They are organisms that acquire their carbon from reduced, preformed organic molecules from other living organisms.

High temperature short time (HTST) is defined as the heating of milk and other liquid food products at high temperatures and at varying time intervals that can range from seconds to minutes and hours in order to inhibit or kill pathogenic microorganisms and other spoilage microbes present in them.

High-throughput techniques are series of experimental procedures that incorporates an array of advanced equipments/instruments and molecular biology protocols including genomics, proteomics, fluxomics, metabolomics and the rest for the sole purpose of generating large amounts of Omics data that helps scientists to better understand the metabolic and cellular activities of microorganisms at the system level.

Histiocytes are macrophages found in connective tissues.

Holoenzymes are the complete catalytic enzyme molecules that comprises of the apoenzymes and cofactors.

Homeostasis is defined as the process of maintaining an appropriate internal environment in a living system.

Homofermenters are lactic acid bacteria that carryout homolactic fermentation.

Homolactic fermentation is the type of lactic acid fermentation in which sugars such as lactose are entirely converted to lactic acid. In this type of fermentation, only one end-product is produced.

Hops are aromatic plants that give beer its flavour and bitterness; and they are naturally sourced from the female flower plant known as Humulus lupulos.

Host-parasite relationship is an association that exists between two organisms known as the host and the parasite in which both organisms either derive benefit from the relationship or is harmed in the process.

Humus is a complex dark or dark brown organic substance resulting from the breakdown of plant and animal material in a process called humification.

Hyaluronic acid is tissue cement found in bones and muscles and which are broken down by hyaluronidase.

Hyaluronidase is tissue-degrading enzymes produced by some pathogenic bacteria.

Hybridization is the process of forming a double stranded DNA molecule between a ssDNA probe and a target single stranded DNA fragment.

Hybridomas are cells capable of continues proliferation, and such cells possess the immortal growth features of cancerous plasma cells otherwise known as myeloma cells.

Hydrogen sulphide test is a biochemical test that is used to identify bacteria that produce the gas, hydrogen sulphide (H2S).

Hyper-endemic diseases are seasonal diseases that often increase in occurrence from an endemic status to a near epidemic status in a particular population. Example of such a disease is common cold which usually rises gradually in occurrence during the cold seasons.

Hypersensitivity is a condition that causes the body to respond very strongly especially in an undesirable manner to allergic substances or allergens. It can also be referred to as allergy or allergic reaction.

Hypersthenuic urine is defined as a urine sample with a high specific gravity.

Hyperthermophiles are thermophiles that grow at optimum temperatures of 80oC and above.

Hyphae is a tubular, long branching filament of fungal cells which bears the reproductive structures of fungi and also help fungal cells to absorb nutrients from their substrates.

Hyposthenuic urine is defined as a urine sample with a low specific gravity.



Idiotypic determinants are antigenic determinants found in the variable regions of antibodies. They are also known as idiotypes.

Immobilization is a biotechnological approach that is used to immobilize or attach macromolecules inclusive of proteins, enzymes and DNA or genes to solid surfaces or structures.

Immune system is generally a complex system of network of cells, tissues and organs and cell products (e.g. antibodies and cytokines) which work cooperatively to protect the body from invading pathogenic microorganisms and the disease/infection that they cause.

Immunity is a state of the host’s body that is characterized by the body’s ability to remove or counteract any trace of non-self (antigens) that enters the system.

Immunization is the administration of antigenic preparations of live or weakened microorganisms (i.e. vaccines or toxoids) especially through parenteral means to an individual in order to confer immunity against particular pathogenic microorganisms.

Immunogenicity is the ability of a substance to elicit an immune response (both humoural and cell-mediated immunity), and this phenomenon is usually exhibited by immunogens.

Immunogens are antigens that induce the production of antibodies by the immune system.

Immunology is an aspect of microbiology that concerns itself with the study of the immune system in man and animals.

Immunology is simply defined as the study of how the immune system of a living organism functions in either a disease condition or a healthy state.

Impellers are structures in fermentation vessels which are used to bring about agitation (i.e. appropriate stirring of the fermentation medium with other mixtures in the vessel).

Imperfect fungi are fungi that reproduce by asexual reproduction. They are generally known as anamorphs; and can be called fungi imperfecti.

Impetigo is an infection of the superficial layers of the skin.

In vivo delivery is the gene therapy technique that delivers DNA, RNA or therapeutic protein directly into the cell or tissue of an organism.

Incapacitating agents are drugs that make people unable to think clearly or that cause an altered state of consciousness (possibly unconsciousness).

Incidence is the number of new cases of a disease that is reported in a given community.

Incidence is used to describe the number of new cases of a disease that is reported in a given community.

Incidence rate is the number of new cases of a disease amongst individuals in a community at a particular time period.

Index case of a disease is the first case of a disease recorded in an epidemic in a particular population.

Index rate is the next estimate to a rate or the best available approximation to a true value. It is usually used when it becomes difficult to count directly the number of people at risk of acquiring an infection in a population.

Indicator organisms are microorganisms that signify the possible contamination of food or food products as well as other materials or environment. They are organisms whose presence in food can be an indication of poor hygiene and sanitation or inadequate organisms.

Indole test (Tryptophan hydrolysis) is a biochemical test that is used to identify Enterobacteria that breakdown tryptophan (an amino acid) to produce indole.

Induced mutations are mutations caused by mutagens (including biological, chemical or physical agents). It is an alteration in the genetic make-up of an organism that is deliberately undertaken for a specific or given purpose.

Inducers are compounds that are necessary for the production of specific bio-product by the microbe but have no impact on the growth of the organism.

Industrial microbiology is the branch of microbiology that deals with the application of microorganisms for the production of products or goods that are of economic importance to man, plants, animals and the environment. It is an area of applied microbiology which deals with the screening, improvement, management, and exploitation of microorganisms that are of industrial importance including bacteria, yeasts, moulds, actinomycetes and viruses for the production of various useful end products that are of economic importance on a very large scale.

Infection is the initial entry of disease-causing microorganism or pathogen into a susceptible host.

Infectious diseases are diseases which occur in a host when there is a change in its normal state of health in which part or all of its normal body functions can no longer carry on.

Infectivity period is the period of an illness during which the infected host is infectious (i.e. disseminating the causative agent of the disease to susceptible hosts). It is the state of infectivity or infectiousness (i.e. the state of being communicable or infectious with a pathogen).

Infectivity which also means infectiousness is the state of being communicable or infectious with a pathogen. It is the percentage of exposed individuals who eventually becomes infected by a particular disease-causing organism (pathogen).

Inflammation is a non-specific immunological response in which the body responds to microbial invasion or tissue injury (e.g. wound or burns).  It usually involves a complex series of immunological response (comprising of both the humoral and cellular immunity) that help to ward-off the establishment of an infection and thus initiate the repair processes of the damaged tissues. It is usually characterized by redness, swelling/oedema, heat, pain and loss of function of the affected body part.

Inhibition zone is the marginated circle of bacterial growth produced around the antimicrobial disk due to antimicrobial action that inhibited the growth of the organism.

Inhibitor compounds are compounds that inhibit or stop a particular metabolic pathway in the microorganism. They are usually added to the fermentation medium to stop the production of unwanted metabolites that are usually the final product of certain metabolic pathways.

Innate immunity is the body’s natural inborn resistance to infection and it is quick in responding to invasive microbes. It is a component of the immune system that is an inherited protective mechanism, and which protect the body of an animals from many kinds of pathogens.

Inoculating loop is a rod or piece of apparatus that is used to transfer organisms from one place to another in the microbiology laboratory. It is generally used to carry out inoculation.

Inoculation is the microbiology technique which is used to introduce or place specimens and microbial cultures on or into a culture medium.

Inoculum is the organism to be transferred into or onto the surface of the culture media.

Inoculum size is defined as the number of invading pathogenic microorganisms that is sufficient enough to initiate an infectious process (i.e. an infection) in a susceptible human host.

Insulin is a hormone produced by the islets of Langerhans in the pancreas; and it is primarily responsible for controlling the way in which our body converts sugar or glucose into useful energy.

Intercalating agents are mutagens that may insert between bases in DNA, causing frame shift mutation during DNA replication. Ethidium bromide (EtBr) is a typical example of an intercalating agent.

Interference is defined as the prevention of the replication of one virus by another.

Interferons are proteinous substances produced by host cells especially in response to a viral invasion or infection; and they generally help to limit the spread of the virus in the host’s body.

Interphase is the stage in which the eukaryotic cell is not experiencing any form of cell division.

Intrinsic factors are those innate factors associated with food and which encourage the growth of microbes that cause disease and the spoilage of the food. They are food-related factors such as pH, nutrient composition and moisture content that influences the growth of microbes in food.

Intrinsic factors of food spoilage are those inherent factors that are associated with the food and which in several ways affect the overall physical and chemical composition of the food. They are food-related factors; and they include the nutrient makeup of the food, the acidity or alkalinity of the food, water activity, moisture content, buffering capacity and the pH of the food.

Isolation technique is a microbiology procedure which is used to obtain pure cultures of microorganisms especially from a mixed culture or specimen through continuous streaking on solid culture media plates.

Isosthenuic urine is defined as a urine sample with a normal specific gravity.



Ketonuria is a condition in which there are abnormal levels of ketone/ketone bodies in urine.

Kilning is a malting technique that involves a controlled drying of the barley grains in hot air for about two days; and it helps to stop further enzymatic activity in the grains in such a manner that does not permanently affect the endogenous enzymes of the grains.

Krebs cycle is the cyclic system that comprises of several enzymatically catalyzed reactions that play significant biological role in the metabolic activities of living organisms inclusive of prokaryotic and eukaryotic cells. It can also be called tricarboxylic acid (TCA) cycle or citric acid cycle.

Kupffer cells are macrophage-like cells found in the liver.



Lactic acid bacteria (LAB) are a group of Gram positive, non-sporing bacteria that carryout lactic acid fermentation of carbohydrates or sugars to produce lactic acid.

Lag phase represent the stage in the development of a bacterial cell when no growth occurs. It is the period after the initial seeding, culturing or inoculation of a bacterium in a fresh culture/growth medium before observable growth begins.

Landfills are land sites meant for the disposal of solid waste materials. It is the oldest form of waste treatment or disposal; and the wastes are usually buried into the soil in such sites or heaped upon previously deposited solid wastes.

Leachate is the fluid portion of municipal solid wastes that squeezes out from the dumpsites and finds its way into groundwater or the surrounding environment.

Leaching is the process of extracting substances such as metals from a solid like metal ore by dissolving them in a liquid medium, either in nature or through an industrial or chemical process.

Leishmaniasis is the parasitic disease caused by the protozoal organism, Leishmania; and the disease affects the skin, spleen and the liver, and it is usually characterized by extensive lesions on the skin (in the mouth, throat and nose region) that sometimes leads to deformity of the affected body part.

L-form bacteria are group of bacteria with defective cell walls.

Lichen is simply a symbiotic association of slow-growing microorganisms that is composed mainly of a fungus and cyanobacteria or green algae.

Liposomes are artificial spherical vesicles that posses several or at least one lipid bilayer for the incorporation of an active agent such as a drug. It is known as closed bilayer phospholipid systems.

Listeriosis a food borne illness (gastroenteritis) caused by Listeria monocytogenes in humans.

Lithotrophs are organisms that utilize or oxidize inorganic compounds to generate their carbon or energy. They obtain their energy from reduced inorganic compounds.

Log phase is the period in the growth curve of a microorganism in which the growth of the bacteria increases at an exponential time. This stage of microbial growth is also known as exponential growth phase; and it is characterized by doubling of the bacterial cells.

Loiasis (Calabar swelling) is a parasitic disease characterized by swelling in the subcutaneous tissue of affected human hosts; and it is cause by Loa loa, a filarial eye worm known.

Long-acting anticoagulants are poisons that prevent blood from clotting properly, which can lead to uncontrolled bleeding.

Lophotrichous flagellation is a type of flagellation found in bacterial cells with flagellum arranged as a tuft (in mass) and distributed over the cell surface of the organism. Such manner of flagellation can also be called peritrichous flagellation.

Lymphatic system is a series of vessels that are primarily responsible for the transportation of lymph fluids (i.e. pale-like biological liquids containing WBCs amongst other substances) from the tissues via the lymph nodes and into the entire circulation of blood in the body.

Lymphocytes are mononuclear leukocytes that mediate both humoural or antibody-mediated immunity and cell-mediate immunity. B cells, T cells and natural killer (NK) cells are the main types of lymphocytes that make up the immune system.

Lysis is defined as the rupture or physical disintegration of a cell.

Lysogenic cycle of viral replication is defined as a type of virus life cycle that

Lysogens are bacterial cells that harbour a viral prophage and can produce bacteriophages under normal environmental conditions.

Lysogeny is defined as a relationship in which a virus or phage genome remains within its host cell (e.g. a bacterial cell) after infection and reproduces alongside the host genome instead of taking total control of the host cell and destroying it in the process of replication.

Lytic cycle of viral replication is defined as a type of virus life cycle that results in the lysis of the host cell.    



Macroconidia are large conidia of fungi.

Macrogametocytes are the female gametes of the Plasmodium parasite.

Macromolecules are large biological molecules that are made up of repeating smaller biological units generally known as monomers.

Macronutrients are those nutrients that are required in large amounts by all forms of life; and examples of macroelements include carbon (C), nitrogen (N), hydrogen (H), phosphorus (P), sulphur (S) and oxygen (O).

Macrophages are multi-functional immune system cells that have a variety of immunological functions. They include Kupffer cells and histiocytes.

Major histocompatibility complex (MHC) molecules are a large set of cell surface protein molecules that are controlled by a collection of polymorphic genes known as the major histocompatibility complex (MHC) which are located on chromosome 6 in humans and on chromosome 17 in mice. They are also known as human leukocyte antigens (HLA) complex.

Major histocompatibility complex (MHC) restriction is simply defined as the ability of the T cells (i.e. CD4+ and CD8+ cells) to specifically recognize antigenic peptide molecules presented by the right type of MHC molecules either Class I or Class II molecules.

Malting is defined as a controlled partial germination of the cereal grain or barley. Malting helps to develop amylases and proteases in the barley.

Mantoux test is a skin test used as a laboratory diagnostic aid to detect reactions of individuals to tuberculin derived from cultures of tubercle bacilli or mycobacteria.

Mashing is defined as the process in which the milled malted grains are mixed with water at an optimal temperature required for the hydrolytic enzymes to act on them.

Mast cells are granulated tissue cells derived from the bone-marrow and which initiate rapid inflammatory response. They resemble basophils, and mast cells release inflammatory mediators which activate vasodilation and the migration of phagocytes to sites of inflammation.

Matrix assisted laser desorption/ionization time of flight (MALDI-TOF) is a high-throughput molecular biology technique that is primarily used to measure the masses of peptides in biological samples (e.g. serum) during protein identification.

McFarland Turbidity Standard is a turbid solution that contains a mixture of barium salt, distilled water and tetraoxosulphate (VI) acid (H2SO4); and it is used to compare and balance the turbidity of both the test and control microorganisms in the microbiology laboratory prior to microbiological analysis especially when carrying out an antibiogram. Generally, it is used to as a reference to adjust the turbidity of bacterial suspensions so that the number of bacteria will be within a given range.

Medical bacteriology is a branch of medical microbiology that is concerned with the diagnosis, prevention and treatment of infectious diseases caused by bacterial pathogens. It is simply the study of bacteria that are of medical importance i.e. that cause diseases in human beings.

Medical virology is simply defined as the study of viruses that are of medical importance i.e. those group or families of viruses that cause disease in humans.

Megakaryocytes are multi-nucleated large cells that are produced in the bone marrow with the sole biological function of producing platelets or thrombocytes, blood-clotting factors.

Meiosis is the type of cell division that occurs during the formation of gamete cells (e.g. spermatozoa and ova).

Membrane filters are filters with varying pore sizes (usually in the range of 0.1-10 µm), and they are used to remove the vegetative forms of microbes (excluding viruses) from solutions. They are thin films made up of cellulose nitrate, cellulose acetate, nylon, polycarbonate or polyvinylidene materials.

Membrane filters are thin films made up of cellulose nitrate, cellulose acetate, nylon, polycarbonate or polyvinylidene materials. They are thin sheets or layers which hold back microorganisms (e.g. bacteria) when fluids are passed or drawn though it.

Membrane filtration technique is a technique that uses a physical barrier (usually a porous membrane or filter) to separate particles and microorganisms suspended in a fluid sample including food, air and water.

Memory B cells are unique class of B cells that remain inert but viable in the blood circulation for a long period of time; and they are capable of rapid activation upon the encounter of a previously invading pathogen or antigen in the body.   

Memory cells are cells of the immune system that help it to recognize similar pathogen in a second attack of the body.

Merozoite is the form of the Plasmodium parasite that invades the red blood cells immediately after its release from the rupturing of schizonts in the liver cells.

Mesophiles are microorganisms that grow best at temperature ranges of 14 or 20 to 45oC. They are generally referred to as mesophilic microorganisms.

Metabolic pathways are series of chemical reactions catalyzed by enzymes and which occur within the cells of living organisms.

Metabolism is simply defined as the summation of the chemical reactions that occurs in the cell at each point in time.

Metabolomics is the quantitative measurement of the metabolome of an organism or the cell. It is the complete set of small molecules, metabolites or metabolic intermediates found in a cell or an organism.

Metallo-beta-lactamases (MBLs) are beta-lactamase enzymes produced by pathogenic bacteria, and which hydrolyzes the carbapenems (e.g. imipenem, meropenem, and ertapenem) and render the antibiotics ineffective for treatment.

Metaphase is the stage of mitosis in which the chromosomes are arranged in the center of the mitotic spindle fiber.

Methanogenesis is the process in which methane (CH4) gas is produced through an energy yielding process that is mediated by certain organisms in the domain Archaea under anaerobic conditions.

Methanogenesis is the process in which methane (CH4) gas is produced through an energy yielding process that is mediated by certain organisms in the domain Archaea under anaerobic conditions. They have the ability to metabolize carbondioxide and hydrogen to CH4 under anaerobic conditions.

Methanogens are obligate anaerobic organisms (members of the domain Archaea) that occur in a variety of environments including rumen (stomach) of ruminant animals and in muds. These organisms are critical for anaerobic digestion processes either in living systems (as obtainable in the rumen of ruminant animals) or in non-living systems such as in sewage or waste water treatment; and they are notable for the production of methane (CH4) gas.

Methicillin resistant Staphylococcus aureus (MRSA) is defined as a pathogenic Staphylococcus aureus strain that is resistant to methicillin and other beta-lactam antibiotics such as oxacillin.

Methyl red test is a biochemical test that is used to identify pathogenic bacteria that produce several acids including acetic acid, formic acid and lactic acid from glucose phosphate through the mixed acid fermentation pathway.

Metulla are short extensions or cell branches which bear one or more phialides in the conidiophores.

Microaerophilic bacteria are organisms that grow in the presence of a very low level of oxygen concentration.

Microarray is usually a solid slide that is immobilized with DNA oligomers (particularly complementary DNA, cDNA molecules). It can also be called a gene chip.

Microbial energetics is defined as the mechanisms by which bacteria and other microbial cells derive the energy they require for growth from their environment.

Microbial metabolism refers to all the chemical changes occurring in a microbial cell during its growth and development for optimal and stable maintenance. They are metabolic intermediate molecules synthesized by microorganisms during and after their growth; and they include primary and secondary metabolites.

Microbial physiology is simply defined as the study of the cell structure, growth factors, metabolic activities, nutritional requirement and the genetic composition of microorganisms.

Microbial weathering is defined as the weathering or rock dissolution that is mainly mediated by microbial activities in the earth’s surfaces.

Microbiologists are scientists that specialize in the study of microorganisms.

Microbiology is the study of organisms that are too small to be seen clearly with the naked eye inclusive of some macroscopic organisms.

Microconidia are small conidia of fungi.

Microgametocytes are the male gametes of the Plasmodium parasite.

Microglia cells are the macrophage-like cells that are found in the brain.

Micronutrients are those nutrients that are required by all forms of life in small amounts or in moderate amounts by some forms of life; and typical examples of microelements include molybdenum, manganese and copper. They can also be known as trace elements.

Microorganisms are organisms that are too small to be seen by an unaided eye; and they include bacteria, fungi, viruses, protozoa and algae.

Microscopy is the microbiological technique of using the microscope to observe cells or organisms that are too small to be seen with the naked eyes.

Milling is a technique used to crush the barley malt or grains in such a way that their husks are not completely removed.

Mineralization is the process by which organic matter in the environment is broken down into inorganic matter.

Minimal inhibitory concentration (MIC) is the lowest concentration of drug that inhibits the growth of the organism.

Minimum bactericidal concentration (MBC) is the lowest concentration of the drug that can kill the test pathogenic bacteria. It is the lowest concentration of a drug that will kill a pathogenic bacterium.

Missense mutation is a mutation in which a base substitution could result in an amino acid substitution. It is a mutation that results in the formation of a faulty protein following the alteration of a single codon during DNA replication.

Mitochondrion is a membrane-bound organelle that is mainly responsible for cellular respiration or energy generation in eukaryotic cells. It is the power house of a cell because of its biological role in energy generation within the cell.

Mitosis is the type of nuclear or cell division in which the mother cell divides into two identical daughter cells.

Mixotrophs are organisms that exhibit mixotrophic mode of nutrition because they combine the metabolism of heterotrophs and chemolithoautotrophs to obtain their energy and carbon.

Mixotrophy is a mode of metabolism or nutrition in which microorganisms obtain their energy and carbon from the oxidation of inorganic substrates and organic substrates respectively.

Molecular biology is the study of the genetic makeup of organisms at the level of deoxyribonucleic acid (DNA). It encompasses the study of the ways in which diseases and traits can be passed through the genes especially via from parents to their offspring’s.

Monoclonal antibodies are homogenous antibodies produced in the laboratory by a single clone of cells (known as hybridoma cells), and all of which exhibit the same antigenic specificity. Monocytes are nucleated leukocytes that exhibit phagocytic action following the invasion of antigens or pathogenic bacteria into the body.

Monomers are the foundational constituents from which macromolecules are formed. For example, amino acids are the monomers of proteins.

Monotrichous flagellation is a type of flagellation found in bacterial cells with only one flagellum at either (both) ends of the cell.

Morbidity is defined as the occurrence of infection (without death) in a particular community. It is used to describe nonfatal and fatal diseases in a population.

Morbidity rate is the number of cases of a particular disease in relation to the entire population under study.

Mortality is defined as the occurrence of death from a particular disease in a given population.

Mortality rate is a measure of the frequency of occurrence of death (resulting from a given disease) in a particular population over a specific period of time.

Most probable number (MPN) is a quantitative analysis that is used for estimating the number of viable microorganisms (usually bacteria) suspended in a given liquid sample including food sample, water sample and soil sample. It is a statistical enumeration technique that is used to estimate the numbers of coliforms present in samples including food, water and milk.

Moulds are filamentous-branching forms of fungi that also bear conidia or fungal spores.

Multicellular cells are cells that may contain different cell types that are organized into tissues and organs that perform specific functions in the host.

Multidrug resistant bacteria (MDRB) are bacterial strains that are resistant to a wide variety of antibiotics inclusive of the beta-lactams, the fluoroquinolones, macrolides, aminoglycosides and sulphamethoxazole-trimethoprim.

Multidrug-resistant tuberculosis is tuberculosis infection caused by M. tuberculosis strains that are resistant to at least one of the two best first-line TB treatment drugs (isoniazid and rifampin).

Mushrooms are macroscopic fungi that possess fruiting bodies with umbrella shapes.

Mutagenesis is the careful alteration of the genetic information of an organism’s genome in such a way that it will result in a mutation.  It is the creation of genetic change in the DNA of an organism and, which will result in the production of a population of cells with an entirely new genetic make-up.

Mutagens are biological, chemical or physical agents that cause mutation in an organism’s genome. They are biological, physical or chemical agents that change the genetic materials (inclusive of DNA and RNA molecules) of an organism and thus increase the frequency of mutations above the natural background level.

Mutant is an organism whose genetic make-up (or genome) has been altered. It is an organism whose genome carries a mutation.

Mutation is a change in the genetic make-up (or DNA) of an organism. It is an inheritable alteration in the nucleotide sequence (or genome base sequence) of a living organism. It is the alteration of the genetic information of an organism.

Mutualism is a type association in which both organisms in the relationship benefits from each other.

Mycelium is a mass or network of hyphae. They are generally a collection of intertwined or knotted hyphae that penetrates the supporting medium or environment on which the fungus is growing. It is the long branching structures of a fungal hyphae.

Mycobiont is the fungal partner in a lichen community.

Mycolic acid is a lipid-containing long chain fatty acid that makes up the cell surface of mycobacteria.

Mycology is the study of fungi.

Mycoplasmas are wall-less bacteria.

Mycoses are infections caused by pathogenic fungi.

Mycotoxicology the area of microbiology that studies fungi and the toxins they produce.

Mycotoxicoses are caused by mycotoxins (fungal exotoxins) produced by some fungal organisms that infest food especially cereals and grains. It can also occur via the inhalation of fungal spores.

Mycotoxins are exotoxins produced by fungi.

Myxomycetes are the acellular slime moulds.



Naked viruses are viruses that do not have envelopes.

Narrow spectrum drugs are antimicrobial agents that have activity against a few groups of pathogenic microorganisms. Such agents can target either Gram-positive bacteria or only Gram-negative bacteria.

Natural killer (NK) cells are large granulated lymphocytic cells of the immune system which are found in the blood circulation, and which are primarily saddled with the responsibility of identifying and killing virally-infected cells.

Naturally acquired active immunity is the immunity acquired by an individual following prior exposure to an antigen or pathogenic microorganisms. This type of immunity is acquired by natural infections caused by pathogens inclusive of bacterial and viral agents.

Naturally acquired passive immunity is the immunity acquired when antibodies are transferred from one animal host to another especially from mother to child transplacentally. It is the type of immunity a child or newborn acquires from the mother through the placenta or breast milk.

Necrotizing fasciitis is an inflammation of skeletal muscles.

Nephron is the functional unit of the human kidney.

Nerve agents are highly poisonous chemicals that work by preventing the nervous system from working properly.

Neurotoxins are toxins found in nerve tissues where they cause neurological damages (e.g. in the pathogenicity of Clostridium tetani).

Neutralization test is an antigen-antibody based test which is used to assay viral infectivity by determining whether a virus has been neutralized by a specific antibody.

Neutrophiles are microorganisms that grow best at pH of between 5.5 and 8.0.

Neutrophils are a type of granulocytes which exhibit both phagocytic and inflammatory immunological response. They are a type of white blood cell (WBC) with an irregular nucleus, and which can attack and kill invading pathogenic bacteria.

Nitrate reductase is an enzyme that breakdown nitrate (NO3) to nitrite (NO2).

Nitrate reduction test is a biochemical test that is used to identify pathogenic bacteria that have the ability to convert nitrate (NO3) to nitrite (NO2).

Nitrification is the biological oxidation of ammonia with oxygen into nitrite. And this is usually followed by the oxidation of nitrites (NO2) to nitrates (NO3).

Nitrite reductase is an enzyme that breakdown nitrite (NO2) to nitrogen (N2).

Nitrogen cycle is defined as the biogeochemical cycle by which nitrogen is exchanged between the biosphere, lithosphere, atmosphere and hydrosphere components of the earth.

Nitrogen fixation is defined as the biological process in which atmospheric or molecular nitrogen (N2) is readily made available in the form (e.g. ammonia) in which it can be accessed by plants and other living organisms in the ecosystem.

Nitrogen fixing bacteria are microbes such as Rhizobium species that fix nitrogen in symbiotic association in leguminous plants including beans and peas.

Nitrogenase is an enzyme that is found in nitrogen–fixing bacteria such as Nitrosomonas and Rhizobium; and which help these organisms to reduce nitrogen (N2) to ammonia (NH3).

Nitrogenous base is a molecule that contains nitrogen and has the chemical properties of a base.

Nitrogenous biological oxygen demand (NBOD) is the amount of oxygen consumed during the oxidation of nitrogenous compounds by nitrifiers or nitrifying bacteria to nitrate and other oxidized products.

Non-infectious diseases are those diseases that cannot be transmitted naturally from one individual to another either directly or indirectly.

Nonsense mutation is a mutation that occurs when the codon for an amino acid is automatically changed to a nonsense (stop) codon. It is a type of mutation in which a prematurely type of shortened protein molecule is formed. This type of mutation results in the production of stop codon.

Normal microflora are microorganisms that colonize the internal and external body surfaces of humans without causing any pathological damage themselves. They are normal microorganisms that naturally inhabit specific sites of the body without causing infection or disease to the host.

Northern blotting technique is used to identify the RNA sequence (i.e. mRNA) of interest in a biological sample; and it allow investigators to determine the molecular weight of an mRNA and to measure the relative amounts of the mRNA present in different samples.

Nosocomial infections are defined as hospital-acquired infections (i.e. infections or diseases acquired by patients few hours after hospitalization). They can be also referred to as healthcare-associated infections (HAIs).

Nosocomial infections are diseases or infections that are hospital-associated and develop inside a clinic facility, and are acquired after a prior stay in the hospital environment.

Notifiable diseases are those diseases that must be reported by law to the appropriate health authorities of a particular population so that appropriate action will be taken by the authorities to avert the spread of the disease. Such disease may affect human beings, plants or animals; and their suspected occurrence or happening in any part of a community must be reported without delay to the appropriate health authorities that will take action directed towards their proper containment and/or eradication in the affected population.

Nucleases are degradative enzymes that cut, shorten and degrade nucleic acids (inclusive of DNA and RNA).

Nucleic acids are macromolecules that store, process and transmit hereditary or genetic materials between organisms.

Nucleoid is the part of a prokaryotic cell that contains the genetic material (DNA) of the organism. It is the bacterial chromosome, and can be referred to as the nuclear area of a prokaryotic cell.

Nucleolus is a specialized structure in the cell nucleus of most eukaryotic organisms formed from regions of chromosomes.

Nucleoside is one of the four (4) DNA bases (i.e. adenine, guanine, cytosine and thymine) covalently attached to the carbon-one (C1) position of a sugar molecule such as the pentose sugar.

Nucleotides are generally the main building blocks from which the DNA polymerase or Taq Pol enzyme synthesizes a new DNA strand. They can also be called deoxynucleosides triphosphate (dNTPs); they include deoxyadenosine triphosphate (dATP), deoxycytidine triphosphate (dCTP), deoxyguanosine triphosphate (dGTP), and deoxythymidine triphosphate (dTTP).

Nucleotides are nucleosides with one or more phosphate groups covalently attached to the 3′ or 5′-hydroxyl group(s) (OH) of a pentose sugar.

Nucleus is the control center of the eukaryotic cell that contains deoxyribonucleic acid (DNA).

Null cells are immature B cells that have not encountered an antigen. They can also be called naïve B cells or lymphocytes.  

Nutrients are substances required for energy production and other biosynthetic activity necessary for the unperturbed growth of microorganisms.



Obligate intracellular parasites are organisms that only replicates inside a living host cell.

Okazaki fragments are short pieces of DNA molecules produced during the replication of the lagging strand during DNA replication.

Oliguria is a decrease in the volume of urine.

Omics is a collection of fields or studies that looks at the cellular functions, structure and genetic make-up of an organism.

Onchocerciasis is a parasitic disease that is characterized by the formation of nodules on the skin (skin dermatitis) and other inflammatory reactions which can lead to blindness in affected human host; and it is caused by the filarial worm, Onchocercia volvulus.

Ookinete is the actively moving zygote form of the Plasmodium parasite that enters the stomach of the female Anopheles mosquito to form an oocyst under the outer lining of the mosquitoes’ gut. Ookinete is the zygote that is motile.

Ophthalmia neonatorum is an eye infection that commonly affects newborns, and the disease is contracted from an infected birth canal (vagina) or cervix. It is caused by the bacterium Chlamydia trachomatis; and it can also be called neonatal ophthalmia.

Opportunistic mycoses are fungal infections caused by opportunistic fungi that only affect people with weakened immune system such as HIV/AIDS patients.

Opportunistic pathogens are microorganisms that causes disease in the absence of normal host resistance i.e. when the immune system of a host is weakened or compromised by a disease (e.g. AIDS).

Opsonization is the deposition of opsonins on the surfaces of pathogenic microorganisms or antigens so that they can be readily phagocytosed by phagocytic cells.

Optical density is a measure of the decrease in transmitted light when light is passed through a microbial suspension or sample.

Oral thrush is a localized fungal infection caused by Candida albicans in the oral cavity of humans such as the tongue, lips and gums. It can also be called oral candidiasis.

Organic solvents are agents that damage the tissues of living things by dissolving fats and oils.

Organotrophs are organisms that obtain their energy from organic compounds. They are organisms that utilize or metabolize organic forms of carbon.

Origin of replication abbreviated as Ori is the particular site where DNA replication begins on a double stranded DNA molecule.

Osmometer is an instrument/equipment that is used to measure the osmotic pressure of cell culture flasks.

Osmophilic organisms are organisms that have the ability to grow in environment with very high concentration of solutes such as sugar and salt. They are microorganisms that can grow in environments with high sugar or salt concentrations; and they can also be known as osmophiles.

Osteoclasts are macrophages found in the bone.

Outbreak is a medical term which is used to describe the sudden and unprecedented incidence of a particular disease in a specific community over a short time period.

Oxidase test is a biochemical test that is used to identify microorganisms that produce the enzyme, cytochrome-c oxidase.

Oxidation-reduction reaction is a type of reaction that occur in living systems in which electrons are transferred from one substance or molecule to another especially in scenarios where energy is either released for cell activities or for storage purposes. Such a reaction can also be known as redox reaction.

Oxidative phosphorylation is defined as the phosphorylation of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) using energy or electrons derived from the electron transport chain (ETC).

Oxygen cycle is defined as the biogeochemical cycle by which oxygen is exchanged between the biosphere, lithosphere, atmosphere and hydrosphere components of the earth.



Pandemic diseases are epidemic diseases that have a widespread reach, affecting more than one country. It is an increase in the occurrence of a series of epidemics within a large population of people that cut across continents of the world.

Paragonimiasis is a pulmonary disease (lung-fluke infection) caused by protozoan species (flukes or trematodes) of the genus Paragonimus species (e.g. P. westermani).

Parasitic relationship is one in which one organism, the parasite, lives off of another organism, the host, harming it and possibly causing death.

Parasitism is a type of relationship in which one partner (known as the parasite) benefits at the expense of the other partner (known as the host) in the association.     

Parasitology is the study of parasites or worms and even insects or arthropods that act as transmission vehicles or vectors for infectious diseases and their causative agents in both human and animal populations. It is study of parasites.

Parenteral drugs refer to therapeutic agents that are not given through the mouth (i.e. orally) but via injections.

Pasteurization is the process of heating milk and other liquid-sensitive liquid below 100oC and at temperatures of about 60-80oC in order to inhibit or kill pathogenic microorganisms present in them. It is also used to reduce the amount of spoilage bacteria or fungi present in food especially during their production. It is the process of heating milk to destroy food spoilage organisms and microbes that cause food borne diseases or infection present in them.

Pathogen is any microorganism which by direct contact and invasion causes disease in another living organism (e.g. animals and human beings). They are disease-causing microorganisms and they include: bacteria, virus, protozoa and fungi.

Pathogenic bacteria are microorganisms or bacteria that cause disease in animals, plants and humans.

Pathogenicity is simply defined as the ability of a pathogen to cause a disease. It is the percentage of individuals in a population who develop clinical disease without necessarily becoming severely sick. It is the mechanism of infectious disease development caused by a microbe (in this case a pathogenic bacteria) in a human host

Pathogenicity islands are the regions of bacterial chromosome (usually of foreign origin) that contain clusters of genes that provoke virulence in the microbe.

Pathogens are disease-causing microorganisms.

Penicillin-binding-proteins (PBPs) are transpeptidases which catalyze the cross-linking reaction between two stem peptides – N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG).

Peptidoglycan is a polysaccharide molecule that consists mainly of alternating repeats of N-acetyl-glucosamine (NAG) and N-acetyl-muramic acid (NAM). It can sometimes be called murein.

Perfect fungi are fungi that carryout sexual reproduction. They are generally known as teleomorphs.

Periodontal membrane is the membranous covering around the teeth, and it can also be called periodontium.

Periodontitis is defined as the microbial infection of the periodontal membrane leading to pyorrhea, and resulting in the teeth falling out if left untreated. It is the inflammation of the periodontium.

Petroleum microbiology is the branch of microbiology that studies microbes that metabolize hydrocarbons and how they could be employed in oil prospecting and oil spillage control.

Phagocytes are generally known as bacteria-eating cells. They engulf microbial cells (particularly pathogenic bacteria) through a process known as phagocytosis. They are specific white blood cells (WBCs) that surround, ingest and destroy other pathogenic microorganisms or cells (e.g. bacteria) that enter the body. They eat bacteria through the process of phagocytosis.

Phagocytosis is simply the immunological process mediated by some immune system cells such as macrophages and neutrophils engulf or ingest bacteria and other particulate materials. It is the immunological process through which particulate matter, foreign bodies or antigens are engulfed, ingested and degraded or broken-down.     

Pharmaceutical microbiology is the branch of microbiology that focuses on all aspects of pharmacy especially as it relates to the manufacture and quality control of pharmaceuticals such as drugs, vaccines, and medical devices. It is an applied branch of microbiology that focuses on the study of microorganisms that are directly or indirectly involved in the manufacture of pharmaceutical products.

Pharmacodynamics is the study of the effects of drug on the body. It explains what therapeutic agents do to the body.

Pharmacokinetics is simply the study of how the body reacts to therapeutic agents or drugs over a period of time. It investigates what a therapeutic agent or drug does to the body after being administered.

Pharyngitis is sore throat infection or inflammation of the sore throat.

Phenotype is the physical and observable characteristic of an organism. It is the observed outcome of gene expression in an organism.

Phialides are non-septate, colourless or pigmented conidia formed form vegetative hyphae.

Phosphorus cycle is defined as the biogeochemical cycle by which phosphorus is exchanged between the biosphere, lithosphere and hydrosphere components of the earth.

Phosphorylation is the formation of a phosphate derivative of a molecule (e.g. ATP).

Photolithotrophic autotrophs are microorganisms that utilize light energy and carbondioxide (CO2) as their sole energy and carbon sources respectively.

Photoorganotrophic heterotrophs are microorganisms that utilize light and organic compounds to generate their energy and carbon molecules required for growth.

Photophosphorylation is another mechanism of ATP generation that is driven by energy derived from sunlight. In photophosphorylation, ATP synthesis occurs via light energy; and it is only common in phototropic organisms (i.e. organisms that carryout photosynthesis).

Photosynthesis is the process by which green plants and other photosynthetic cells manufacture their own food and energy in the presence of sunlight and carbondioxide (CO2).

Phototrophs are organisms that get their energy from the sunlight.

Phycobiont is the cyanobacteria partner in a lichen community.

Phylogeny is the branch of science that studies the evolutionary correlation amongst organisms using the genetic information encoded in their nucleic acids (i.e. DNA and RNA).

Physiology is defined as the study of life processes in living cells.

Phytochemicals are the chemical compounds produced by trees and plants, and which have the ability to delay the onset of some chronic diseases. They are the non-nutritive or nutritive, biologically active compounds present in edible natural foods including fruits, vegetables, grains, nuts, seeds, tea and plants.

Phytopathogens are fungal organisms that cause disease in plants especially agricultural crops.

Phytoplanktons are aquatic plants which serve as source of food some aquatic organisms such as the larva of mosquitoes.

Phytoremediation is the use of plants in situ (i.e. at the site of contamination), their enzymes or enzymatic systems, their roots and other associated microbes to degrade pollutants present in the environment (soil, water and air).

Pili are structures which help to transfer genetic material (DNA) from one bacterial cell to another.

Plaque assay is a technique that is used to determine the concentration of infective particles in a virus solution or sample; and it is usually expressed as plaque-forming units per ml (pfu/ml).

Plaque is a naturally-occurring or constructed biofilm that is comprised of bacteria and are normally found on the surfaces of the teeth. It is the area of lysis or hole formed in a lawn of cells in cell/tissue culture due to the infection or replication of a virus.

Plaque-forming unit is defined as the number of plaques formed per unit of volume or weight of a virus suspension or sample.

Plasma cells are antibody-secreting cells produced by immunocompetent B cells.

Plasma is the red blood cell free-fluid portion of blood which contains all the clotting factors of blood. It consist of H2O containing a large number of dissolved substances, including proteins, salts (Na, K, Chlorides, and bicarbonates), food materials (glucose, fats, amino acids), hormones, vitamins, and excretory materials.

Plasma membrane is a selectively permeable structure that surrounds the contents of the cell and regulates the movement of materials in and out of the cell. It is present in both eukaryotic and prokaryotic cells.

Plasmids are extrachromosomal DNA molecules found in both eukaryotic and prokaryotic microorganisms that have the ability to replicate independently.

Point mutation is a mutation that changes the base-pair of a codon. It is caused by the loss or gain of a single base-pair or as a result of amino acid substitutions in a base-pair. They are mutations that change only one base pair of a nucleotide sequence.

Polyclonal antibodies are heterogeneous antibodies produced from different clones of B cells.

Polymerase chain reaction (PCR) is the molecular biology technique that is used to amplify or copy specific gene sequences or nucleotides of a DNA molecule or gene.

Polypeptide is a chain of amino acid sequence held together by a type of covalent bond known as peptide bond (-CO.NH-).

Polyuria is an increase in the volume of urine.

Population is a collection of people or organisms of the same type. Population in epidemiological terms can also be used synonymously as community.

Porin channels or porins are proteins that assemble to form a complex that acts as channel where molecules including substrates and antibiotics can pass through the cell of an organism.

Prebiotics are non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improve the health status of the host.

Precipitation reaction is an immunological reaction in which an antigen reacts with antibodies known generally as precipitins to form visible clumps or precipitates.

Precipitation reaction is the immunological interaction of a soluble antigen with a soluble immunoglobulin molecule (precipitin) to form an insoluble complex.

Precursors are chemicals or substances such as amino acid that get directly incorporated into the end-product; and they are usually added to the fermentation medium at the beginning of the process or at a later stage in the fermentation process.

Predation is defined as the phenomenon in which the predator attacks and kills the prey.

Preservation is the process of preventing microbial growth in manufactured products e.g. canned foods, pharmaceuticals and medications using preservatives.

Preservatives are antimicrobial agents or chemical substances that delay the overgrowth or growth of microbes in either sterile or non-sterile products.

Prevalence is used to describe the total burden of disease in a community. It is used to show the old and new infections that occur in a population at a given time.

Prevalence rate is a measure of the new and old cases of a disease reported in a community at a given time period. It is the total number of persons infected by a disease in a population at a given time irrespective of when the disease occurred.

Primary lymphoid organs are the central organs of the immune system in which the maturation of the immune system cells (particularly the B and T lymphocytes) primarily occurs. They serve as sources of lymphocytes for other components of the immune system; and they include the bone marrow and thymus.

Primary metabolites are substances secreted by microbes at during their exponential (log) phase of growth; and which are very essential to the growth, development and reproduction of the microorganisms.

Primers are short DNA fragments (usually about 18-20 bases or nucleotides long) that contain specific sequences which are complementary to the template DNA molecule to be copied and amplified.

Prions are sub-viral infectious entities that consist mainly of proteins. They are unique infectious particles that lack nucleic acids inclusive of DNA and RNA. They are subcellular proteinous (infectious) molecules which are neither viruses nor viroids, and which cause a range of diseases in humans (e.g. Creutzfeldt-Jacob disease, CJD).

Probiotics are live cultures of bacteria which boost the normal microbial flora of the human gastrointestinal tract, and thus improve the general health of the gut. They live microorganisms (especially bacteria and fungi) that when administered in adequate amounts confer health benefits to the host taking it.

Prokaryotic cells are microbial cells that have chromosomes that are not separated from the cytoplasm by a membrane. They are cells that lack a nucleus and other membrane-enclosed organelles like mitochondrion and chloroplast.

Promoter region of a gene is the regulatory element of the gene that controls the transcription of the coding region.

Prophage is the latent form of the virus genome that remains within the host cell without destroying it.  

Prophase is the first stage of mitosis; and it is the stage in which the chromosomes of the parent cell condense in order to separate into two sister chromatids.

Proportion is an expression of an event in which the numerator is always included in the denominator. It is always expressed as a percentage.

Proteins are macromolecules comprising mainly of amino acids; and they play critical biological roles in living systems such as for the repair of damaged tissues and also for growth. They are macromolecules that comprises of repeating chains of amino acids which are held together by peptide bonds.

Proteome is the total number of proteins encoded by the genome of an organism. It is the protein complement of the genome of a cell.

Proteomics is the measurement of the protein function of an organism in relation to its gene expression.

Proton motive force (PMF) is defined as the energized state of a membrane that is created by a protein gradient. It is the inherent energy produced within the inner mitochondrial membrane of the mitochondria during oxidative phosphorylation, and which is vital for several mechanical and chemical works in the cell.

Protozoa are single-celled eukaryotic microorganisms that lack cell wall and are motile.

Protozoology is the study of protozoa or parasites.

Pseudohalitosis is a state in which there is actually no clear evidence of bad breath even though the individual think he or she may have halitosis.

Psychrophiles are microorganisms that can grow best at a very low temperature e.g. 0oC to 12oC. They are usually found in environments that are constantly cold or frozen.

Psychrotolerant microorganisms are microorganisms that can withstand low temperatures or cold conditions such as that obtainable in a refrigerator.

Psychrotrophs are microorganisms that grow at 0oC to 7oC but have a maximum temperature of around 35oC and an optimum temperature of between 20 and 30oC. They are mostly implicated in the spoilage of refrigerated foods.

Public health is defined as the wellbeing of the general public. It is the field of medical science that maintain a surveillance and monitoring function over the general population by probing the water supply, food and other materials that enters the human body in a view to  keep them safe from pathogens and also to prevent the spread of infectious diseases through them in a defined human population.

Public health microbiology is the branch of microbiology that deals with the monitoring, control and spread of infectious diseases and pathogens from community to community, country to country and around the world.

Puerperal fever is the sepsis that usually occurs after childbirth.

Pulmonary anthrax is the anthrax that affects the respiratory system.

Punctiform is a bacterium that is less than 1 mm in size; and it can also be called a pin-point organism.

Pure cultures are cultures or microbial growth in which all the microorganisms on solid culture media are of the same strain or species. Pure cultures can also be known as axenic cultures. It is the progeny of a single cell.

Purines are heterocyclic aromatic organic compound that consist of a pyrimidine ring fused to an imidazole ring. They are the larger of the two types of bases found in DNA. The other bases are known as pyrimidines.

Pustule is defined as a small elevation of the outer skin layer containing pus. And it can also be called boil or abscess.

Putrefaction is the microbial decomposition of organic matter (such as the anaerobic breakdown of proteins) with the production of foul-smelling compounds.

Pyelonephritis is the infection of the kidney.

Pyrimidines are aromatic heterocyclic organic molecules or compounds found in living organisms.

Pyrogen is defined as a fever-causing (inducing) agent that includes toxins of microorganisms.

Pyrogen test is defined as a test that detects the presence of bacterial endotoxins (lipopolysaccharides) in a given product or sample including food, air, parenteral drugs and other pharmaceutical or medical products and devices.

Pyrogenicity is simply defined as the ability of a pyrogen to cause infection or disease.

Pyrogens are fever-causing (inducing) agents that include toxins of microorganisms. They are the lipopolysaccharide (LPS) component or endotoxins of bacteria especially Gram negative organisms.

Pyuria is the presence of pus cells (or dead white blood cells) in urine.



Quality assurance (QA) is a planned and systematic process used for evaluating and monitoring the quality and appropriateness or suitability of a product or given service.

Quality control (QC) is defined as a monitoring system that is used for detecting and correcting analytical errors by establishing performance limits. It is a procedure or set of procedures intended to ensure that a manufactured product including pharmaceutical and medical products or performed services adheres to a defined set of quality criteria or meets the laid down requirements of the products.

Quality control strains are typed cultures of microorganisms with known antimicrobial susceptibility patterns and which are used to ensure consistency, accuracy and reproducibility of a particular susceptibility test. They can also be called reference strains.

Quarantine is the medical practice of limiting the free movement of patients that has been screened and confirmed to have a highly communicable disease (e.g. tuberculosis which is caused by a species of Mycobacterium). The sole reason for quarantining an individual with an infectious disease is to prevent the spread of the pathogen and the disease to susceptible members of the public, while the infected person is carefully treated and supervised to ensure that the disease is totally eradicated.

Quorum sensing is defined as the cell-to-cell interaction (communication) between one bacterium and another which allows them to share genetic information through the release of signaling molecules (e.g. acylated homoserine lactones, AHLs) that enables them to evade inconveniences in their surrounding environment.



Rancidity is defined as a type of food spoilage that occur in food or food products with high lipid content; and it is mainly characterized by the production of fatty acids.

Rate measures the possibility or probability of occurrence of some particular episode (e.g. disease or infection) in a given community/population.

Ratio is the relationship between a numerator and a denominator.

Recombinant DNA (rDNA) technology is the in vitro controlled manipulation of nucleic acids (DNA and RNA) in order to produce new gene products or a combination of genes with improved biological function. It can also be called genetic engineering.

Recombinant DNA molecule is the DNA molecule formed when two DNA molecules from two separate organisms are genetically modified and fused together.

Re-emerging diseases are old infectious diseases that are known but have surfaced again after a significant decline in their incidence in the past.

Remote sensing is defined as the scientific and computerized technique of gathering images (or data) of the earth’s surface from the space (satellites) and transforming same into maps that are used to investigate the co-distribution of a disease within a defined human population.

Renaturation is the second stage of the PCR reaction. This stage is also known as annealing, and it is the stage in the PCR reaction in which the reaction process is rapidly cooled to a temperature of around 50-65oC for 20-40 seconds.

Replication fork is the site on a double stranded circular DNA molecule where the double strands unwound for the replication of each of the separated single-strands.

Replication is defined as the process in which a cell divides to make copies of its genome or itself.

Replicon is the portion of the genome of an organism that contains the origin of replication. During DNA replication, the replicon is usually replicated as a unit.

Reporter gene assay is a molecular biology technique that is used to evaluate the expression and regulatory potential of an unknown gene sequence. The reporter gene assay is generally used to study the expression of a gene.

Reservoirs are human or animal populations in which a disease-causing agent is preserved in a viable infective stage, and from which healthy individuals in a population may be infected.

Resident microflora are those microorganisms which are permanent dwellers or natural inhabitants of a particular environment or body at any given point of time.

Restriction endonucleases are enzymes that cut nucleic acids (inclusive of DNA and RNA molecules) at specific sites.

Restriction sites are the different sites on a DNA molecule that is nicked by a particular restriction enzyme.

Reticuloendothelial system (RES) is a collection of macrophages (or mononuclear phagocytes) that are found in specific organs of the body where they help to get rid of antigens and other microbial cells from the body’s circulation of blood. Examples include spleen and liver.

Reverse transcriptase enzyme is an enzyme that catalyzes the transcription of RNA into DNA

Reverse transcription is the genetic process of copying the genetic information found in the RNA genome of an organism into DNA.

Rheumatic fever is an autoimmune disease involving the joints.

Rheumatoid arthritis is a chronic systemic inflammatory autoimmune disease generally characterized by swelling and pain in the joints of our body.

Rheumatoid factors are autoantibodies produced in the body of rheumatoid arthritis patients. It is an IgM class of antibody.

Ribosomes are the protein synthesizing machinery of a cell.

Ribozymes are RNA molecules that function as catalysts and/or enzymes in living organisms, and they are found in both eukaryotic and prokaryotic cells – where they help to process RNA precursor molecules especially during protein synthesis. They can also known as catalytic RNA.

Riot control agents (tear gas) are highly irritating agents normally used by law enforcement agents for crowd control or by individuals for protection (for example, mace).

Risk factors are environmental issues or personal tendencies that increase one’s probability or chance to acquire a disease or an infection in a defined population. Examples of risk factors include diet, alcohol use, cigarette smoking, and obesity.

RNase enzyme is a nuclease enzyme which digests RNA.

Root caries is the loss of the root portion of the tooth.



Sabouraud’s dextrose agar (SDA) is a selective culture medium that is used for the selective isolation of fungi from both environmental and clinical samples. This medium is usually prepared with the incorporation of antibiotics and other antimicrobial agents that allow only fungi to grow, while inhibiting the growth of other microbes such as bacteria.

Sampling is defined as the statistical process of selecting a part or portion of a whole product batch to represent the entire batch.

Sanitization is the process of reducing microbial populations on inanimate surfaces or objects to levels adjudged as safe or microbial free.

Sanitizers are antimicrobial agents used to achieve sanitization in a given environment; and sanitizers unlike other antimicrobial agents (e.g. disinfectants and antiseptics) only reduces the microbial population of inanimate objects to safe levels tolerable for usage, and barely eliminates (i.e. kill or inhibit) the infecting pathogens.

Satellitism is the observable effect seen when certain growth-factor-requiring microbes (such as Haemophilus influenzae) grow efficiently on a growth media which lacks the required growth factor but which supports the growth of another microorganism which can provide the required growth factor required for the primary organism (H. influenzae) to grow. It can also be called satellite phenomenon.

Scaling up is defined as the processes involved in the increasing scale of operation culminating in the production plant or a bioreactor. It is the conversion of a laboratory procedure to an industrial process – in which desired products are produced in large quantities.

Scarlet fever is a widespread skin rash.

Schistosomiasis is a blood-fluke infection (tropical disease) that mainly affects the urinary and intestinal tracts of people living in poor rural communities of both tropical and subtropical countries including Africa, the Middle East, Asia, and the Americas; and it is caused by Schistosoma species.

Scientific method is the general approach that involves series of systematic steps used by scientists (including microbiologists) to conduct research and to achieve reproducible results.

Sebum is the oily substance produced by the sebaceous gland of the skin.

Secondary lymphoid organs are specialized organs or tissues where lymphocytes continue their maturation after their first production in the primary lymphoid organs. It is within the secondary lymphoid organs that the lymphocytes (i.e. the B and T cells) proliferate and differentiate into effector cells that actually neutralize invading pathogens or antigens.

Secondary metabolites are substances secreted by microbes during the end of the exponential growth phase of the microbe or near the stationary phase of growth, and which do not play a role in the growth, development, and reproduction of the microbes.

Selective media are culture media that promote the growth of certain type of bacteria while inhibiting the growth of the undesired organisms.

Selective toxicity is the ability of an antimicrobial agent to be injurious to a pathogenic microorganism (i.e. kill or inhibit the growth of the microbe) without being detrimental to the recipient host.

Semi-continuous cell lines are cell lines that contain the same number of chromosomes as the parent cells from which they are derived.

Semi-continuous fermentation is defined as the fermentation process in which the substrate is added and the product removed at intervals.

Sensors are structures fitted to a fermentation vessel which help to control environmental parameters such as pH and temperature. They also help to monitor the level of fermentation medium in the fermentor.

Septate hyphae are hyphae with cross-walls.

Serial dilution is the laboratory technique of making lesser concentrations of a given solution from its original stock solution (usually having a much higher concentration). In serial dilution, the further you dilute the original solution; the subsequent tubes will have half the concentration of the initial tube (i.e. the tube preceding it).

Serum is the yellowish/golden fluid that remains after blood coagulates, and the red cells have formed clot. It is plasma minus the clotting factor fibrinogen.

Sexually transmitted diseases are diseases transmitted through sexual intercourse especially when sex is done unprotected with an infected person. Gonorrhea and syphilis are examples of such diseases.

Siderophores are low-molecular weight iron-chelating compounds synthesized and exported by most microorganisms including fungi and bacteria for the uptake of iron in their environment.

Signs are changes in a diseased individual which can be physically observed. Examples include rash on the body, rise in body temperature and boils.

Silent mutation is a mutation that has no effect on the phenotype (or physical appearance) of an organism. It usually results in the formation of a normal protein.

Single cell proteins are simply defined as microbial-derived proteins which are generally used by humans and animals as food supplements or food.

Single-stranded DNA binding proteins are special type of protein molecules that bind the separated single strands of DNA molecules in order to keep it separated until the individual strands have been completely replicated.

Slime moulds are motile amoebic organisms and they differ from fungi phylogenetically even though they may resemble fungal organisms in some way.

Soil is simply defined as the mixture of minerals, organic matter, gases, liquids, and the countless macroscopic and microscopic organisms that together support life on the earth’s crust (lithosphere).

Soil microbiology is the branch of microbiology that studies microorganisms that are found in the soil and how they can be exploited to the benefit of mankind such as in improving the fertility of the soil and in the production of useful products (e.g. antibiotics). It is the study of microorganisms (bacteria, archaea, viruses, fungi, parasites and protozoa) in the soil, their functions, and how these microbes affect the properties of the soil.

Soil-borne pathogens are microbes that are found in the soil and which cause disease in humans and animals.

Solid culture media are culture media that contain agar, the solidifying agent of culture media.

Somatic gene therapy is the gene therapy technique that target body cells.

Source of a disease is the site or material from which a disease-causing agent is immediately transferred to a susceptible human host either directly or indirectly.

Southern blotting technique is used to identify the DNA sequence (gene) of interest in a biological sample; it allow investigators to determine the molecular weight of a restriction fragment and to measure its relative amounts in different samples.

Soxhlet extractor is a piece of laboratory equipment that is designed for the processing of certain kinds of solid materials including plant materials; and it is used for the extraction of desired compounds from materials which have a limited solubility in a solvent, and whose impurity  is also insoluble in the solvent.

Spargers are devices used for forcible aeration in aerated stirred tank batch fermentors.

Species are collections of strains of an organism that have many stable attributes in common, and which notably differ from other groups of strain.

Spectrophotometry is a method used to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through a sample solution.

Spectrum of an antimicrobial agent refers to the range of pathogenic microorganisms to which a particular drug is active against.

Spoilage organisms are microbes whose growth and proliferation in food creates undesirable characteristics such as change in colour, texture, odour and taste.

Spontaneous generation (abiogenesis) is the hypothesis that living organisms are capable of emanating from non-living things.

Spontaneous mutation is a mutation that occurs on its own in an organism without the support of a mutagen. It occurs naturally and occasionally in a microorganism and usually in the absence of any added chemical or physical mutagen.

Sporadic diseases are those diseases that occur irregularly and at a periodic or random interval amongst susceptible members of a population. Such diseases do not occur frequently but rather occasionally in a given community, and they show immediate clinical signs and symptoms amongst affected susceptible hosts in a population.

Sporangiospores are asexual spores produced by zygomycetes.

Spores are the resistant inactive structures formed by some prokaryotic and eukaryotic organisms.

Sporicidal agents are antimicrobial agents that destroy the spores of microorganisms and kill spore forming microbes.

Sporostatic agents are antimicrobial agents that inhibit spores or spore formation.

Sporozoite is the infectious form of Plasmodium parasite, which is injected into humans by the bite of female Anopheles mosquitoes.

Staining is any microbiological process which increases the contrast of organisms when certain dyes or stains are applied to them prior to their examination under the microscope.

Staphylokinase is an enzyme that acts by breaking down the fibrin component of blood in a process known as fibrinolysis; and it is mainly produced by pathogenic Staphylococcus aureus.

Starch is the form in which carbohydrate is stored in plants.

Stationary phase is the period in the growth curve of microorganisms (bacteria) in which the growth of the microbial cells stops. The stationary phase is characterized by a slow growth of bacterial cells due to nutrient depletion and toxic waste buildup in the growth medium.

Statistics is a branch of mathematics that is concerned with the proper method of collecting, organizing, presenting, analyzing and interpretation of numerical data.

Steeping is a malting technique in which the barley grains are soaked in water for about two days.

Stem cells are self-renewing cells found in the bone marrow and which undergo cell division to differentiate and proliferate into other important cells inclusive of the immune system cells and blood cells.

Sterility simply means the absence of living organisms including bacteria, fungi, viruses, protozoa and other vegetative cells in a product.

Sterility tests are microbiological and/or biochemical tests carried out on biological products, food and other pharmaceutical products in order to critically assess their freedom from contaminating microorganisms including mycoplasma, bacteria, fungi and viruses.

Sterilization is defined as any process by which objects, materials or an environment may be rendered sterile (i.e. completely free from all forms of life). It is the process by which all living cells, viable spores, viruses and viroids are either destroyed or removed from an object or habitat.

Sterilization technique is used to make microbial culture media, reagents and other objects or apparatuses in the microbiology laboratory sterile. And it is mainly carried out with the autoclave.

Stop codons are codons that signal the end or termination of the translation process of a protein synthesis coding sequence on the mRNA.

Strain improvement is defined as the process of improving the production and yielding capacity of a microorganism through certain (deliberate) technological microbiological, biotechnological or biochemical process.

Strains are a population of microorganisms that differ distinguishably from at least some other population of organisms within a given taxa.

Streaking is a microbiological technique that is used to obtain pure cultures of microorganisms (particularly bacteria) in the laboratory. It usually involves a series of drawing a wire loop (carrying an inoculum of the test organism or sample) back and forth on dried solid culture media.

Streptokinase is an enzyme produced by Streptococcus species and which help pathogenic Streptococcus species to spread in the tissues of the body by hydrolyzing coagulated human blood plasma. They can also be called fibrinolysin; and they have a similar activity with staphylokinase produced by pathogenic S. aureus.

Streptolysin O is an immunogenic, haemolytic and cytolytic toxin produced by S. pyogenes.

Streptolysin S is a non-immunogenic, haemolytic, oxygen-stable toxin produced by S. pyogenes.

Subcutaneous mycoses are fungal infections that affect the subcutaneous tissues below the skin, and the bone and other tissues occasionally.

Substrate-level phosphorylation is the phosphorylation of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) independent of the electron transport chain (ETC). In substrate level phosphorylation, ATP is produced directly from an energy-rich compound such as glucose when the energy-rich compound or intermediate is being hydrolyzed or broken down in its catabolic pathway.

Sugar (glucose) utilization test is a biochemical test that is used to detect bacteria that ferment various sugars (e.g. glucose) as well as convert pyruvate (the end product of glycolysis) into gaseous by-products (e.g. hydrogen and CO2). It can also be called carbohydrate fermentation.

Sulphur cycle is defined as the biogeochemical cycle by which sulphur is exchanged between the biosphere, lithosphere, atmosphere and hydrosphere components of the earth.

Superficial mycoses are fungal infections which are only limited to the keratinized outer layer of the skin, hair and nails.

Surface enhanced laser desorption/ionization time of flight (SELDI-TOF) is a proteomic technology routinely used in molecular biology laboratories for the rapid identification of biomarkers specific for cancerous cells in the proteomes of both tissue fluids and body fluids such as blood and urine.

Surfactant is a chemical substance or an organic compound that lowers the surface tension between two liquids.

Surveillance is an epidemiological technique of observing, recognizing and reporting a disease outbreak to the appropriate authority (e.g. state or local ministry of health, WHO, the CDC and other public health agencies) as they occur in order to forestall their sporadic spread to an uninfected community.

Susceptibility (antibiotic) disks are specially made paper disks which are impregnated with known concentrations of antimicrobial agents (e.g. antibiotics), and which are used in the laboratory to test and determine the efficacy of a drug against pathogenic microorganisms prior to therapy.

Symbionts are organisms that take part in a mutualistic relationship.

Symbiotic association is a relationship that exists between two or more different organisms in which both organisms benefit from or one organism is harmed as a result of the relationship.

Symptoms are physically observed signs of a disease. They are changes that occur during the development of a disease in an individually, and they are experienced by an individual in the form of pain, fatigue, loss of appetite and body discomfort.

Synbiotics are defined as appropriate combinations of probiotics and prebiotics.

Syndromes are a set of clinical signs that a characteristics of a particular disease. They give impetus to the presence of a disease which warrants laboratory diagnosis. The syndrome of a disease is a combination of its signs and symptoms.

Syphilis is a sexually transmitted disease (STD) that is caused by a spirochaete called Treponema pallidum.

Systemic mycoses are fungal infections that affect deep tissues and organs of the body; and they generally start off as pulmonary infections in affected individuals.



T cells are lymphocytes that mature mainly in the thymus after production in the bone marrow; and they express T cell receptors (TCRs) for the recognition of antigenic peptide molecules displayed by major histocompatibility complex (MHC) molecules. They are the main mediators of cell-mediated immunity (CMI).

Taeniasis is a parasitic infection of the small intestines of humans, and it is caused by a range of protozoa generally known as tapeworms.

Taq polymerase enzyme is a heat-stable DNA polymerase enzyme that is isolated from a thermostable bacteria (particularly Thermus aquaticus), and which is used in PCR techniques to extend primers along the single stranded DNA molecule in the 5′-3′ direction.

Taxon is a group of strains, species or genera that have similar morphologic or physiological characteristics different from other category of organisms in a given taxonomic classification.

Taxonomy is the scientific system of classifying biological organisms into taxa.

Teleomorphs are fungal organisms with sexual characteristics.

Telophase is the fourth stage of mitosis; and it is the stage of cell division after anaphase.

Temperate phages are bacteriophages that can infect a bacterial (host) cell and establish a lysogenic relationship instead of immediately killing or lysing the infected host cell.

Teratogens are other classes of mutagens – which are known to cause harm to the foetus or embryo during pregnancy.

Tetanospasmin is a plasmid-encoded neurotoxin produced by Clostridium tetani; and it is the main virulence factor of Clostridium tetani infection. Another name for tetanospasmin is tetanus toxin.

Tetanus is an acute localized non-communicable disease of man and animals characterized by muscle spasm caused by spores of Clostridium tetani that enters the body from the soil through a wound infection.

Thallus is the vegetative body of fungi.

Therapeutic dosage is the concentration of antimicrobial agent that is clinically relevant for treating a particular microbial disease.

Therapeutic dose is defined as the drug level that is required for clinical treatment of a particular infection.

Thermophiles are microorganisms that grow at very high temperatures e.g. at 55oC or higher. Their optimum growth temperature is between 55 and 65oC while their minimum growth temperature is 45oC. Thermophiles are usually found in hot or thermal environments such as hot springs and boiling water containers or heaters.

Thimble is a porous container and component of a soxhlet extractor that helps to hold the solid material so that the extraction solvent can saturate it and pass through it, thereby extracting the compound of interest from the solid material or sample.

Thymectomy is the medical procedure of removing the thymus through surgery.

Tonsillitis is an inflammation of the tonsils.

Top fermenting yeast are yeast cells such as Saccharomyces cerevisiae that is used for the production of stout or ale beer; and that settles at the top of the fermentor at the end of fermentation.

Topoisomerases are enzymes produced by bacteria, and which removes or introduces negative supercoils to newly synthesized DNA molecules.

Total cell count is an estimate of the total number of both living and dead cells in a given volume of a sample.

Total organic carbon is a measure of the dissolved oxygen consumed by the microorganisms under specific environmental conditions.

Total oxygen demand is a measure of the amount of dissolved oxygen consumed by all the chemical elements in a given water sample when complete (total) oxidation is achieved.

Toxic alcohols are poisonous alcohols that can damage the heart, kidneys, and nervous system.

Toxic dosage of a drug is the concentration at which the agent becomes too poisonous to the recipient host.

Toxigenicity is the ability of bacteria to produce toxins that contribute to the development of a disease.

Toxins are products of microbes which at low concentrations act on cells or tissues of a host to cause systemic damage.

Toxoids are inactivated nontoxic bacterial toxins which are used as antigens to spark immunity in the recipient animal host. They induce the production of antitoxins (i.e. antibodies that destroy or inactivate microbial toxins) in animal host when administered.

Transcription is the synthesis of an RNA molecule (mRNA in particular) that is complementary to one of the 2 single strands (ss) of a double-stranded DNA molecule (dsDNA).

Transcriptomics is the measurement or analysis of the expression levels of the mRNA of the cell. It is the evaluation of the transcription stage of gene expression in an organism in order to monitor the relative level of transcriptome (the total set of mRNA produced in an organism) in the cell.

Transduction is a virus-mediated transfer of exogenous DNA from a donor cell to a recipient cell. In transduction viruses or bacteriophages act as vehicles or vectors that carry the gene of interest into the target host cell. It is simply defined as the transfer of genetic material (i.e. exogenous or foreign DNA molecule) between bacteria by bacteriophages (bacterial viruses).

Transfection refers to the in vitro techniques in which exogenous DNA molecule is introduced into a recipient host cell in order to genetically modify the latter. It is the process of introducing foreign DNA into cells (especially eukaryotic cells) using non-viral vectors.

Transformation is a mechanism of genetic transfer in bacteria in which a piece of free DNA molecule (genetic material) is taken up by a bacterium in its environment and integrated into the recipient genome.

Transgenes are defined as genetically modified genes.

Transgenic animals are genetically modified animals whose genome has been genetically engineered to contain one or more genes or DNA from an exogenous source (especially DNA molecules with desired beneficial function).

Transient microflora are microorganisms which only have a temporary habitation in an environment or body at any given time.

Translation is a genetic process responsible for the production of proteins in the ribosome of an organism using the genetic information in mRNA as a template.

Transmissible spongiform encephalopathy is the fatal prion disease of the nervous system that is characterized by the degeneration of the spongiform of the brain in animals.

Transpeptidation reaction is the chemical reaction that forms the peptide cross-links or bonds during the synthesis of peptidoglycan (murein) in a bacterial cell.

Transplantation is simply the medical procedure of replacing an abnormal or diseased/damaged cell, tissue or organ by a functional and normal one. It can also be called graft or grafting.

Transversions involves the switching of one base type for another base type. For example, pyrimidine can be switched for a purine in transversion mutations.

Triple sugar iron agar (TSIA) is a differential agar medium used to different lactose-fermenting Enterobacteriaceae from non-lactose fermenting Enterobacteria.

Tubercles are small and hard nodules that characterize the tuberculosis (TB) disease.

Tuberculin is a purified protein derivative (PPD) preparation that contains tuberculoprotein – which is usually obtained by the filtration of a culture of tubercle bacilli.

Tuberculosis is a chronic infectious respiratory disease that occurs in both man and animals; and it is caused by the airborne pathogen Mycobacterium tuberculosis.

Turbidity is the measurement of suspended solids (in this case, microbial cells) in a solvent e.g. water or normal saline.

Turbidostat is a continuous fermentation system that is fitted with a photocell that adjusts and regulates the flow of nutrient medium through the culture vessel in order to maintain a constant cell density or turbidity.

Twitching motility is a process which allows bacterial cells to adjust their positions in a biofilm community using pili, a bacterial appendage. It allows bacterial cells in biofilms to come close to each other and move along surfaces effectively; and thus helps bacterial cells to form microcolonies.

Tyndallization is the heat-sterilization of food or food products by a process of alternate heating and cooling.

Type I hypersensitivity is an IgE-mediated type of allergy that occurs immediately following the exposure or prior sensitization of the host’s body by the invasion of an allergen. It can also be called anaphylactic or atopic hypersensitivity reaction.

Type II hypersensitivity is an immediate-type hypersensitivity that is mainly observed in blood transfusion reactions and haemolytic disease of the newborn (HDN). It can also be referred to as a cytotoxic allergic reaction.

Type III hypersensitivity is a type of allergic reaction that is mainly characterized by an adverse inflammatory response mediated by antigen-antibody complexes. It can also be known as immune-complex allergic reaction.

Type IV hypersensitivity is a cell-mediated allergic reaction that induces a localized inflammatory reaction via the release of cytokines. In delayed-type hypersensitivity, sensitized T lymphocytes mediate the release of cytokines (e.g. interleukins and interferons) that recruit macrophages to the site of infection or allergen administration. It can also be called delayed-type hypersensitivity (DTH) reaction.



Ultimate biological oxygen demand is a parameter that quantifiers the amount of oxygen required for the total biochemical degradation of organic matter by aquatic microorganisms including bacteria and protozoa.

Unicellular cells are single-celled organisms (e.g. bacterial cells or prokaryotic cells).

Urease is an exoenzyme that hydrolyzes urea to produce ammonia and carbondioxide.

Urease test is a biochemical test that is used to detect and differentiate Enterobacteriaceae that produce urease enzymes from those organisms that do not produce the enzyme.

Urethritis is the infection of the anterior urinary tract.

Urinary tract infections are bacterial infections caused by the presence and growth of pathogenic bacteria anywhere in the urinary tract system including the kidney, bladder and the urethra.



Vaccination is the injection of a human or animal host with attenuated products of pathogenic microorganisms (generally known as vaccines) in order to stimulate protective immunity in the individual.

Vaccines are live or attenuated preparations of microorganisms which are generally used as antigens to confer immunity in living organisms (particularly humans and animals). They are biological substances that contain attenuated microorganisms and/or antigens to a particular infectious disease, and which are used to protect an individual against the disease in future.

Vacuoles are non-rigid; membrane bound fluid-filled sac or organelles that function as storage space of cells.

Validity is the expression of the degree to which an epidemiological study or test is capable of measuring what it is intended to measure. A test result is valid when the result of such a study corresponds to the truth of the study. It is the lack of bias and confounding factors in a study.

Variolation is a primitive type of immunization/vaccination in which people are inoculated with smallpox fluid from sufferers of smallpox as a way of building immunity against the disease in the recipient host.

Vectors are extrachromosomal DNA molecules or vehicles such as plasmids that are capable of autonomous replication within a host cell; and their primary function is to transport the gene of interest or piece of DNA contained in the plasmid into host cells (e.g. bacteria). They are organisms that transmit disease-causing pathogens to other species of animals, microbes and man. They are living organisms (insects or animals) that help to transmit or carry disease-causing microorganisms from one individual to another.

Venereal disease research laboratory (VDRL) test is the serological test used for the identification of Treponema pallidum, causative agent of syphilis infection in the clinical microbiology laboratory.

Viable cell count is an estimate of the total number of living cells present in a given volume of a sample.

Viral haemorrhagic fevers are viral infections or diseases generally characterized by haemorrhage (bleeding) resulting from various forms of capillary damage of organs of the body; and they are caused by viruses in the Flaviviridae family, Arenaviridae family, Filoviridae family and Bunyaviridae family.

Viral pathogenesis is the ability of a virus to cause infection in its host organism or cell.

Virions are complete virus particles that consist of a single-stranded (ss) or double-stranded DNA or RNA that is enveloped in a protein coat.

Viristatic agents are antimicrobial agents that inhibit the growth of viruses.

Viroids are sub-viral infectious entities that infect plants. They are acellular infectious agents like the prions that lack the essential features of a virus; and which are capable of directing their own replication since they have small naked RNA as their genome. They are small, single-stranded (ss) circular RNA molecules that chiefly cause diseases in plants.

Virology is the study of viruses.

Virucidal agents are antimicrobial agents that kill viruses.   

Virulence factors are microbial products such as toxins that enhances the degree of pathogenicity of a microbe in ah host.

Virulence is the severity, degree or intensity of pathogenicity of a microbe. It is usually the combination of invasiveness, toxigenicity and the state of immunity of the host in relation to the infecting bacterial pathogen.

Viruses are very small infective obligate intracellular parasites that consists of a capsid (protein coat) containing a nucleic acid (DNA or RNA), and that only replicates inside a living host cell. They are non-cellular microorganisms that consist of nucleic acids (either DNA or RNA) which are surrounded by a protein coat.

Voges-Proskauer (VP) test is a biochemical test that is used to identify Gram negative bacteria that produce 2,3-butanediol (acetoin) from the fermentation of glucose.

Vomiting agents are chemicals that cause nausea and vomiting.



Water activity (aw) is the actual amount of water available to microorganisms for growth and survival.

Water for injection is water of extra high quality, which is used for production of parenterals such as infusion solution for intravenous therapy (solution for injection) and water-based ophthalmic (eye) products.

Water microbiology is the branch of microbiology that ensures that the water supply to homes, industries, towns and local communities are of good quality and free from water-borne pathogens such as Escherichia coli, Vibrio cholerae amongst others.

Water quality is defined as the suitability of water to sustain various uses or processes without causing any untoward effect to its users.

Weathering is defined as the breaking down of rocks and minerals on the earth’s surface.

Western blotting technique is used to identify specific antibody proteins that have been separated from one another in a sample; and it allow investigators to determine the molecular weight of a protein molecule and to measure the relative amounts of the protein present in different samples.

Widal test is a serological test which is used to test for the presence of Salmonella antibodies (O and H antibodies) in a patient’s serum, as an aid in the diagnosis of typhoid and paratyphoid fevers.

Wort is defined as the aqueous soluble solution that results from the mashing process.



Xerophilic organisms are organisms that have the ability to grow in environment with low water activity (aW). Xerophilic organisms can also be called xerophiles; and they are organisms that can grow and survive in dry environments especially those with low water activity.



Yeasts are single-celled or unicellular fungi, and they are usually round to oval in shape.



Zoonoses are infectious diseases which can be contracted by human beings and in which the disease-causing agent responsible for the disease is generally maintained in an animal population.

Zoonotic infections (zoonosis) are diseases/infections caused by pathogens that can be passed or shared between humans and animals

Zoophilic fungi are dermatophytes whose natural habitat is animals such as cattle, horses, dogs and cats. Example includes Microsporum species such as M. canis, M. gallinae, M. nanum and Trichophyton species such as T. verrucosum and T. equinum.

Zygospores are sexual spores with thick walls commonly produced from a diploid zygote formed from the fusion of two haploid nuclei (known as the gametangia) or unicellular fungal gametes.

Zygote is the diploid cell formed when the male gamete (microgametocyte) and a female gamete (macrogametocyte) fuse or join together.


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