Scope of Microbiology; Notes on Dental Infection & Microbiology Equipment

Microbiology pioneers

Written by MicroDok


Microbiology is simply defined as the study of microorganisms. Microorganisms or microbes are organisms that are too small to be seen by the naked (unaided) eye. Microorganism is the term applied to all microscopically small living organisms. Original discoveries about microorganisms where made with these early developed microscopes (i.e. the simple microscopes). Microbiology as an applied science developed as a scientific discipline because of the availability of the microscope and the ability to isolate and grow pure cultures of microorganisms (in artificial culture media in vitro) which can be observed or magnified using the microscope. Pure culture is necessary for the proper understanding of the form and development of microorganisms. A pure culture is defined as a population of cells that are identical because they arose from a single cell.

Microorganisms are ancient forms of life that are by and large too small to be seen with the naked eye, and the field of Microbiology is exclusively dedicated to the studying and harnessing of these small forms of life which have immense impact on practically every spheres of life including plants, animals, humans and even the inanimate aspect of the earth. Microbiology, an applied and basic biological science demonstrates in every respect the fundamental principles that align the biological discipline, thus making it the foundation and a center-piece of the biological sciences. The study of microbiology actually began and gained prominence with the discovery of the microscope, a metallic piece of instrument which is used to see microorganisms (invisible forms of life).

Robert Hooke (1843-1910) was actually the first to use the microscope to view the unseen forms of life, making him the first to describe microorganisms. Hooke as shall be seen later in this section reported seeing plant and fungal structures under his crude compound microscope whose lenses were unable to view bacteria. His observations were drawn and recorded in his book titled Micrographia.  However, Antony Van Leeuwenhoek (1632-1723)who is widely regarded as the father of the field of microbiology, was actually the first microbiologist to see and describe bacteria. Therefore, the development of microbiology as a biological science depended on the availability of the microscopes in addition to the ability to isolate and grow pure forms of microorganisms in vitro and in vivo.

There is plethora of microscopes today ranging from simple light microscopes to even complex electron microscopes that give better perspectives about the microbial world. These pieces of equipment allow microbiologists to gain better understanding of microbial cells at the cellular level. Several microbiologists including but not limited to John Needham (contributed to the theory of spontaneous generation), Nicolas Appert (father of canning and discoverer of appertization), Francesco Redi (contributed to the theory of spontaneous generation), Edward Jenner (discovered vaccination), Alexander Flemming (discovered the first antibiotic, penicillin), Elie Metchnikoff (coined the word phagocytosis), Louis Pasteur (discovered pasteurization), Dmitri Iwanovski (contributed to the field of virology), John Tyndall (discovered tyndallization), Paul Ehrlich (discovered antimicrobial agents), Hans Christian Joachim Gram (discovered Gram Staining technique), Joseph Lister (contributed to the principles of antisepsis during surgery) and Robert Koch (formulated Koch’s postulate of disease) amongst others as shall be seen in this section contributed tremendously to the development of the field of microbiology.

The advances in the field of microbiology today is centered on the serendipitous discovery of many pioneer microbiologists who in time past made numerous contributions that scientists after them built upon as aforesaid. Each discovery and invention in the field of microbiology by notable microbiologists has helped to broaden our understanding of the microbial life as well as the economic and medical importance of microorganisms to man and his environment. Our understanding of the microbial world is a continuum in view of the fact that as new species and strains of microorganisms are being discovered some old diseases are now re-emerging; new drugs and vaccines are being discovered; and microbiologists are now more proactive in tackling the untoward effects of microorganisms especially as it has to do with causing diseases.

The beneficial potentials of microorganisms are also harnessed by man to solving some societal problems. Thus it is critical to acquaint ourselves about some notable discoveries in the field of microbiology, the inventors or discoverers and the solid foundation they have laid in making this important aspect of the biological and medical sciences, microbiology to see the light of the day. In this section, the discoveries of some notable microbiologists in time past and their unflinching contributions to the study of microbiology shall be highlighted.


Antony Von Leeuwenhoek (1632-1723): Anthony Van Leeuwenhoek was a Dutch scientist and tradesman who did a part time job as a draper and amateur microscopist while investigating the microbial world whit his crude or simple microscopes. Leeuwenhoek is generally known as “the Father of Microbiology”, and he is also considered to be the first microbiologist since he was the first to observe and describe bacteria with his simple microscope. Leeuwenhoek was a Dutch draper who made significant development in building one of the first microscope used to visualize the invisible forms of life (microorganisms). He observed Animalcules’ in 1675 in feacal samples, water and from soil samples when he was working with his simple lenses. The Animalcules’ observed by Leeuwenhoek with his simple microscope or lenses were later discovered to be bacteria and other microorganisms. The study of bacteria practically began with the use of the microscope, and this singular development is credited to Anthony Von Leeuwenhoek. Leeuwenhoek is considered one of the first scientists to have observed bacteria using the microscope; and this is why he was recognized as the father of microbiology.


Robert Hooke (1635-1703): Robert Hooke was the first scientist to study and record living cells using the microscope. The existence of organisms too small to be seen by the naked eyes had long been suspected even before the discovery of the microscope but there was no particular instrument for their study as at the time until the microscope was discovered. Nevertheless, the discovery of the unseen forms of life (i.e. microorganisms) was linked to the invention of the microscope. Robert Hooke, an English mathematician and natural historian was also an excellent microscopist as at the time the microscope ushered in the field of microbiology. In the first book devoted to microscopic observation, Micrographia, which was Robert Hooke’s first book, Hooke clearly illustrated among many other things, the fruiting structures of microorganisms particularly moulds, which are a type of fungi. His work was the first known description of microorganisms, but the first person to see bacteria was the amateur microscope builder, Antony Van Leeuwenhoek. Leeuwenhoek in 1684 was aware of Hooke’s work, and he used extremely simple microscopes of his own construction to examine the microbial content of a variety of natural substances including water. Though his microscopes were crude as at the time when compared to today’s standards, Leeuwenhoek was able to see bacteria (which is much smaller than moulds) by the careful manipulation and focusing of his microscope. Antony Von Leeuwenhoek discovered bacteria in 1676 while studying pepper-water infusions; and his discovery of the microbial world with his amateur crude-microscopes set the pace for the development of the field of biological sciences known widely today as microbiology. Progress in understanding the nature and importance of microorganisms remained slow for about 150 years after then, until in the nineteenth century when improved microscopes became widely distributed and used for a variety of scientific investigations.


Robert Koch (1843-1910): Robert Koch, a German scientist was the first medical microbiologist. Koch was also the first to establish the actual relationship between the causative agent of a disease and the disease condition itself. Koch ushered in the beginning of bacteriology, an important field in microbiology that studies bacteria; and he is thus regarded as the father of bacteriology because he successfully isolated several disease-causing bacteria and even discovered the animal vectors of a number of human diseases including anthrax. Robert Koch successfully proved in his experiment that Bacillus anthracis caused anthrax, a bacterial disease of cattle and sheep which can be transmitted to humans via contact with infected animals or their products. Thus, Koch was the first to demonstrate and point out the fact that a particular disease is caused by a given microorganism. Anthrax is a disease that occurs primarily in animals but can also occur in humans, and it is thus a zoonotic infection since it can be transmitted from animals to humans. It is a deadly blood disease that occurs in herbivores such as horses, sheep’s and cattle’s when they ingest the spores of B. anthracis during grazing in the fields. Robert Koch’s work on anthrax, tuberculosis (caused by Mycobacterium tuberculosis), rabies (caused by a virus) and cholera (caused by Vibrio cholerae) gave rise to the field of medical microbiology, which today is saddled with the primary responsibility of unraveling the causative agents of microbial diseases of man from clinically important specimens. Koch also confirmed the work of other microbiologists particularly that of Louis Pasteur on the “Germ Theory of Disease” which he took several steps further; even as he independently established “the relationship or link between a particular microorganism and a disease”. This is known as the germ theory of disease – which postulates that a particular microorganism is responsible for the cause of a specific disease. Koch’s criteria became known as Koch’s postulates and are still used today in the medical profession to link a particular disease to a particular microorganism. Robert Koch’s postulates helps microbiologists and other medical and biomedical scientists to establish ways of combating pathogenic microorganisms and finding possible cures for the disease that they cause through the identification of the causative agents of the infection or disease. Robert Koch’s work actually started with a study of B. anthracis, and then later with the culturing of the microorganisms responsible for causing tuberculosis and cholera, Mycobacterium tuberculosis and Vibrio cholerae respectively. Koch’s work on bacteriology is significant because his research saved many people’s lives from diseases such as typhoid, diphtheria, tetanus, syphilis, and anthrax as at the time and even till date; and he achieved this breakthroughs by finding the particular microorganisms responsible for these diseases using his set of postulates (generally known as Koch’s postulates) which are still used even till date both in the field of microbiology and even in aetiology and in the medical sciences to unravel disease causes. Aetiology is the scientific study of the origin and causes of infectious diseases. Microbiologists don’t have to worry about wondering how an infectious disease foments or what actually caused a particular infectious disease because of Robert Koch’s groundbreaking research which shall be highlighted in this section. Because of his work in establishing the link between a disease and its causative agent, Robert Koch was awarded the 1905 Nobel Prize for Physiology or Medicine for his outstanding contributions on tuberculosis. The definite proof that microorganisms could cause disease provided the greatest scientific impetus for the development of the field of microbiology. Koch’s discovery and significant contribution in the field of microbiology led to the development of pure culture techniques, stains, agar/culture media and Petri dishes which complimented the study of microbiology. Koch’s postulates work very well for a handful of pathogenic microorganisms and the diseases that they cause; but however, this pioneering landmark in the determination of the causative agent of a particular disease does not still work well for all pathogenic microorganisms. Some infections or disease do not produce signs and symptoms in the host, and as such makes it difficult to associate such a disease to a particular microorganism. Secondly, some pathogenic microorganisms such as viruses cannot be easily cultured in vitro (i.e. outside a living host or in plates) as is the case with bacteria and fungi (which can easily be cultivated in vitro); and ethical considerations in medical practice disallows the direct inoculation of such infectious agents into human subjects for medical research. However, recent discoveries in microbiology such as gene cloning and recombinant DNA technology amongst others afford microbiologists the chance to isolate and clone the genes responsible for virulence and/or pathogenicity in infectious agents (inclusive of bacteria, viruses, protozoa and fungi). In summary, Koch was renowned for his pioneering works in bacteriology especially in the discovery of the causative agents of some infectious diseases including cholera, anthrax and tuberculosis. He also formulated the Koch’s postulates, devised means for isolation of pure culture and discovered the tubercle bacilli.


Louis Pasteur (1822-1895): Louis Pasteur, a French scientist was the first to report the role of microorganisms in fermentation in 1848. Though a trained chemist, Pasteur was also one of the first scientists to recognize the significance of optical isomers, and he emerged one of the greatest biologists of the 19th century. Louis Pasteur achieved distinction in organic chemistry for his discovery that tartaric acid (a four-carbon organic compound) forms two different types of crystals. He showed that pebrine disease of silkworm was caused by a protozoan parasite. In 1857, he unraveled the mystery of sour wine and showed that bacteria were responsible for the spoilage of wine and other food products. Louis Pasteur demonstrated that alcoholic fermentations were as a result of microbial activity, and that some microorganisms could decrease alcohol yield and sour the product, and that some fermentations were  aerobic while others where anaerobic. Pasteur also developed the process of pasteurization to preserve wine during storage by showing that mid-heating of milk could kill microorganisms in broth. Pasteur firmly disproved the doctrine of spontaneous generation by his swan-necked flask experiment (which shall be highlighted later). He isolated the causative agents of cholera and rabies and subsequently developed vaccines for rabies, cholera, chickenpox and anthrax. Louis Pasteur also proposed germ theory of disease and he also discovered the existence of life in the absence of free oxygen (anaerobic growth). His breakthroughs in microbiology helped solidify the concept of the germ theory of disease, whose principles were being developed at about this time by Robert Hooke and others. Pasteur in 1880 developed a method of weakening a virulent pathogen, and using same to immunize individuals. His work established the roadmap for inoculating people with attenuated microorganisms as a way of protecting them from diseases caused by specific microorganisms.


Ferdinand Cohn (1828-1898): Ferdinand Cohn, a German biologist was born in Breslau (now in Poland). Cohn was the first to classify algae (a type of microorganism), and he is also one of the founders of modern microbiology and bacteriology. Ferdinand Cohn successfully distinguished algae from plants, and he also classified bacteria into four (4) different groups in terms of their characteristic shapes (rods, spirals, spherical and threads); a bacterial classification which is still in use in bacteriology till date. Cohn is one of the founding fathers of the field of bacteriology, and he also provided a basis for the classification of bacteria. He was trained as a botanist and became an excellent microscopist, and this led him to study algae (unicellular plant-like microorganisms) and later, photosynthetic bacteria. Cohn believed that all bacteria were members of the plant kingdom. He discovered that bacteria multiply by dividing into two cells (a process known as binary fission), and that certain bacteria form an extremely resistant structure called endospore in the cell. His work and interest in heat resistant bacteria has led us to know about bacterial endospores. He described the entire life cycle of the endospore forming bacteria, Bacillus (vegetative cell – endospore – vegetative cell), and discovered that the vegetative form of this bacteria was killed by heating, but their endospores were not killed in the process of heating. His work in this area of heat resistant forms of bacteria helped his contemporaries as at the time to know why boiling is an unreliable means of preventing fluid infusions from supporting microbial growth. Cohn is credited with the use of cotton plugs for closing flasks and tubes to prevent the contamination of sterile culture media in the early 1860s. Ferdinand Cohn also studied the large sulphur bacterium, Beggiatoa mirabilis and was the first to identify the small granules present in the cells that are made of sulphur (which are produced from the oxidation of hydrogen sulphide, H2S).


Francesco Redi (1626-1697): Francesco Redi, an Italian scientist was the first scientist to challenge the theory of spontaneous generation by demonstrating that living organisms did not actually originate from non-living things. He developed a scientific experiment to test the spontaneous creation of maggots from fresh meats using two jars (one of the jars was left open while the other was closed). Redi was famously known for his work on spontaneous generation or abiogenesis. He challenged the concept of abiogenesis by showing that maggots on decaying meat came from fly eggs deposited on the meat and not from the meat itself. Redi explained that flies land on exposed meat and lay their eggs which eventually hatch to produce maggots. Redi performed series of experiments in the early 1670’s in which he covered jars of meat with fine lace that prevented the entry of flies into the jars. Because the meat was covered, no maggots were produced, and this led Francesco Redi to drop the notion of spontaneous generation. Francesco Redi successfully challenged and refuted the theory of spontaneous generation through his work on maggot and flies, in which he showed that maggots on meat came from egg flies. Though his work was known, the idea of spontaneous generation was not dropped as other scientist like John Needham continued from where he stopped to unravel the mystery behind it.


John Needham (1713-1781): John Needham is the English scientist who performed experiments on spontaneous generation or abiogenesis in mutton broth and hay infusions. Needham showed that mutton broth boiled in flask and then sealed could still develop microorganisms, which supported the theory of spontaneous generation. He took hot boiling mutton gravy (meat infusion) in a flask and closed same with a cork. He later found the spoilage of the meat infusion and also observed animalcules in it. Needham killed the living matter by boiling and thus concluded that animalcules arose spontaneously from the meat, thus he put forth the notion that microorganisms arise by spontaneous generation. His works were later challenged and repeated by Lazzaro Spallanzani who modified Needham’s experiment by including a longer boiling time in his own experiment.


Abbe Lazzaro Spallanzani (1729-1799): Lazzaro, an Italian naturalist criticized John Needham’s work on spontaneous generation. In 1769, he performed series of experiments on the subject matter which showed that heating can prevent the appearance of animalcules in infusion (depending on the degree of heating). Abbe Lazzaro Spallanzani was not satisfied with Needham’s work of only using cork to seal the flask, and thus he hermetically sealed the flask in order to prevent its content from coming into contact with atmospheric air. He boiled meat and vegetable broth for a very long time in a flask and then sealed the neck of the flask by melting it. As a control, he briefly boiled the contents of some flasks, left some open to the air, and the others partially sealed with corks. After two days, Lazzaro discovered that sealed flask infusions remained barren for long days (and without organisms) while the control flasks were swarming with some organisms. Abbe Lazzaro Spallanzani concluded that organisms will not appear unless new air entered the flask and come in contact with the meat infusion; and he also commented that external air might be needed to support the growth of animals already present in the medium, a notion which was welcomed by supporters of spontaneous generation. His works on this area were very good, but nevertheless, faulty experiments continued to be performed, and evidence was gathered in favour of spontaneous generation. John Needham objected to the findings of Lazzaro with the reason that Spallanzani had destroyed the “vital force of life” with the excessive amounts of heat he applied in his experiments.


Nicolas Appert (1749-1841): Nicolas Appert, a French chef and a confectioner is the “father of canning”, and was the inventor of airtight food preservation which is still applicable today in the food industry. He developed a heating process in which canned foods (e.g. milk, meat, drinks, and vegetables) could be preserved and prevented from spoilage by microbial fermentative action. His method provided a system in which food and other like-products could be sealed in a canned medium for adequate preservation until use. Appert’s crude canning system is still being used till date in the food and beverage industries to can or preserve foods but with some modifications; and his method has significantly contributed to the control of food spoilage and the transmission of food borne diseases through canned food products. His crude method of canning foods included the use of large glass bottles that contained the foodstuff, and the bottles were sealed with corks. Appert’s method shows that sealing foodstuffs in canned containers before heating them reduces the effect of air in causing food spoilage; and that both heating and boiling slows down food spoilage by inhibiting food borne pathogens. He applied Lazzaro Spallanzani’s observation in 1805 for preservation of foods by enclosing them in airtight containers and then heating the containers, a process called “appertization”. Appertization is a method of food preservation in which certain types of food are exposed to a temperature/regime which renders safe for the consumer and microbiologically stable for extended or indefinite periods of time on subsequent storage in hermetically sealed containers at temperatures below 40oC. In honour of his work, canning is sometimes called “appertization”, and this process is quite different from pasteurization – which is the form of heat treatment (especially at temperatures below 100oC) that kills food spoiling microorganisms in milk and other dairy products. Pasteurization unlike appertization (which uses a lower temperature to sterilize food products) heats food products (particularly milk) at a high temperature that is lethal for food-borne pathogens (e.g. Salmonella species) to thrive. However, appertized foods are not necessarily sterile as are pasteurized food products; and this is why foods sterilized by appertization are always kept under refrigeration temperatures for proper preservation. Nicolas Appert was able to preserve highly perishable foods by this process, and canning (which it was later called) was in use in food making even much before its scientific principles were clearly understood. Nicolas Appert had no formal education but his many years of trials- and errors- at his confectionary in France on how best to preserve food paved way for him when he was challenged by the 12, 000 Franc prize offered by the French government to anyone who could develop practical means of preserving perishable foodstuffs. This happened at a time when France led a war against her neighbour’s under its leader, Napoleon Bonaparte in the 18th century. Due to his lack of formal education, Appert had no scientific idea about the chemistry and biology of his invention, appertization (which is now commonly called canning). It was Louis Pasteur that later explained the rationale behind Appert’s method of preserving foodstuffs and why it worked.


John Tyndall (1820-1883): One of the traditional arguments against abiogenesis was the claim that the heat used to sterilize the air or specimens was destroying a vital force of life which did not allow microorganisms to spontaneously appear. People believed for many centuries the concept of spontaneous generation, i.e. the creation of life from organic matter. The proponents of spontaneous generation believed that living organisms could generate from non-living things. John Tyndall, an English physicist conducted his experiments in a specially designed box called “Tyndall chamber” with which he proved that dust carried germs. He showed that dust did carry microbes, and if dust was absent the sterile broth will still remain sterile for indefinite period of time even if it was directly exposed to air. Tyndall’s work in 1877 led to the development a process called “Tyndallization” – which is used for the complete sterilization of food by alternate heating and cooling. He observed that boiling the infusion for more than 5 hours was not sufficient enough to sterilize it, and he concluded that bacteria has both thermo-stable and thermo-labile phases, thus proving the existence of heat resistant forms of bacteria as was also confirmed by Ferdinand Cohn.


Girolamo Fracastoro (1478-1553): While the issue of spontaneous generation lasted as at the time, some other scientist like Girolamo Fracastoro was interested about the transmission of the disease caused by these microorganisms. Girolamo Fracastoro was an Italian scientist, a poet and scholar in mathematics, astronomer and geography, and who in 1546 proposed that epidemic diseases are caused by transferable tiny particles or spores (that does not necessarily need to be living entities but chemicals) that could transmit infection by direct or indirect contact or even without contact over long distances. His work led to the use of the term “fomites” in medicine, a phrase he used to describe things like clothes and linen, which although not themselves infected or polluted, but can nevertheless promote the essential seeds of the contagion and thus cause infection in humans who come in contact with these infected clothes or linen generally known as fomites. Fomites are non-living vehicles (e.g. water, tables, chairs and food) that help to transmit infectious agents and/or diseases to susceptible human or animal hosts. Girolamo had the concept that “contagion is an infection that passes from one thing to another”, and he recognized three phases or forms of this passage as contact, air and lifeless objects or fomites. His idea received credibility that microorganisms were the substance of contagion, and his theory remained influential for nearly three centuries, before being displaced by germ theory. Contagion was the term used by Girolamo when referring to pathogenic microorganisms.


Edward Jenner (1749-1823): Edward Jenner was the pioneer of the dreaded smallpox vaccination and also the father of immunology. Jenner, an English physician in 1798 successfully vaccinated a boy named James Phipps against smallpox (caused by variola virus). Smallpox was a disease that reached an epidemic level in the 17th-18th century, and the disease negatively impacted humanity causing high rates of morbidity and mortality as at the time. Smallpox was at the time treated by a Chinese practice called variolation-which involved the direct injection of smallpox fluid from an infected person into the body of a healthy person as a way of building immunity against the disease in the recipient host. However, Jenner came up with vaccination or immunization, which was a modification of variolation, and involved the injection of cowpox fluid from infected cows into the body of humans.  Though he could not explain the actual cause of the disease, he was honoured in the same year when he developed immunization for smallpox, a disease that is characterized by the production of small lesions called pox or pokes on the skin of the sufferer. Jenner had earlier observed that milkmaids exposed to cowpox never developed the serious smallpox and he thus hypothesized that exposure to cowpox led to protection against smallpox. Variolation, which is immunization against smallpox, was a common practice before vaccination was common as at the time, and this worked because the patient was exposed to a weak strain of smallpox, which did not kill, yet conferred immunity on the host against the disease. Edward Jenner discovered that cowpox could protect against smallpox, with a much lower incidence of complications than variolation. His discovery that a less pathogenic agent could confer protection against a more pathogenic one was indeed remarkable, and his works ushered in the modern era of vaccines and immunization, which is a preventive medicine. Jenner is widely known around the world for his innovative contributions in immunization and the total eradication of smallpox. Mankind does not need to worry about smallpox any longer, a disease that devastated humanity for centuries. His work paved way for the rapid development of vaccine and the scientific field called vaccinology, which today has helped to proffer vaccine candidates for the effective fight of a wide variety of infectious diseases. Pasteur discovered a general method for immunizing people against disease while working on chicken cholera, and he coined the term vaccination to describe this technique. Pasteur’s technique of weakening a strain by a damaging treatment or passing it through a susceptible host was termed “attenuation” and this resulted in the creation of vaccines against anthrax, rabies and other microbial diseases. Many vaccines have been developed over the years and children today receive a number of shots after birth, a practice which is greatly decreasing infant mortality.


Ignaz Semmelweis (1818-1865)Ignaz Semmelweis is regarded as the father of infection control because of his discovery of the cause of maternal death during childbirth. Ignaz introduced an infection control method known as antisepsis to control the contamination of the labour room by pathogenic microorganisms which caused the death of pregnant women during childbirth as at the time. Ignaz was a Hungarian physician, and he showed that child-bed fever was spread by physicians and could be prevented by careful washing of the hands. He realized that blood poisoning agents were transmitted to maternity patients by physicians fresh from performing autopsies in the mortuary, and he also observed that asepsis in obstetrical wards could prevent the transmission of childbirth fever from patient to patient. Ignaz Semmelweis therefore instigated a policy that all attending physicians must wash their hands with chloride of lime, and between patients – as this procedure reduced the spread of disease. Even though he is still remembered for his contributions towards the principle of disinfection (a practices that can stop the spread of disease or infection), his true call for disinfection practices in the medical profession was largely unheeded to as at the time because it implied that physicians were at fault in this case. However, Ignaz’s discovery of aseptic technique or antisepsis in obstetric wards as at the time is still used till date as an important infection control practice in hospitals. And hand washing technique which is one of the most veritable tool in preventing microbial contamination of the hands and the entire body is still being practiced all over the world as the surest way of keeping microbes at bay. The work of Ignaz Semmelweis showed that pathogenic microorganisms can be controlled on the human body and on other abiotic surfaces by using certain antimicrobial agents such as antiseptics and disinfectants to control microbial growth.


Joseph Lister (1827-1912): Joseph Lister, an English surgeon is the father of antiseptic surgery. He was aware of Semmelweis’s work and together with Pasteur realized the true nature of disease cause, transmission and prevention. Lister sought for ways to prevent microorganisms from infecting wounds because deaths resulting from post-surgery infections as at the time was alarming and accounted for more than 40% of the total deaths. This led him to develop a system of surgery which was designed to prevent the entry of microorganisms into wounds. He used dilute solution of phenol/carbolic acid to soak surgical dressings, and he also performed surgery only under or after a spray of disinfectant to prevent airborne infections. After its application in medical practice, Lister’s patients had fewer post-operative infections and this provided indirect evidence that microorganisms were the causative agents of human disease. His published work transformed the practice of surgery, and his experiments on this area is the origin of the present day aseptic technique used to prevent infections and their spread in clinical practices worldwide. In addition, Lister also carried out works on the lactic acid fermentation of milk, in which he demonstrated the specific cause of milk souring. He named the microorganism responsible for causing the souring of milk as Bacterium lactis.


Dmitri Ivanovski (1864-1920): Dmitri Iwanovski was a Russian botanist, and one of the discoverer of filterable nature of viruses and the field of virology. He was one of the founders of the biomedical field called virology. In 1892, he filtered infectious extract from tobacco plants infected with mosaic disease using bacterial filters (which are sieves that excluded bacteria from samples), and found to his greatest surprise that the filtrate was still fully infectious. It was discovered later that diseases in plants and animals was caused by some submicroscopic agents that were smaller than bacteria, and that were retained in the filtrates after passing through the bacterial filters. Dmitri’s work ushered in the field of microbiology which explained a new type of infectious agents called “viruses” – that are capable of permeating porcelain filters, something which bacteria could never do. Dmitri’s findings were studied further by other scientists like Frederick Loefller (1852 -1915), a German bacteriologist who discovered the organism causing diphtheria (Corynebacterium diphtheriae) and the cause of foot and mouth disease (Aphthovirus); F.D Herelle (1873-1949), a French-Canadian microbiologist and F.W Twort (1877–1950), an English bacteriologist who independently discovered bacterial viruses known as “Bacteriophages”. These scientists discovered that this agent (filterable viruses) was quite different from cellular organisms like bacteria whose structure and development are already known. But in 1935, Wendell Stanley crystallized virus and found that it is made up of protein and nucleic acids.


Elie Metchnikoff (1845-1916): Elie Metchnikoff was a Russian biologist, zoologist and protozoologist who is best remembered for his pioneering research work into the immune system, specific cells and organs of the body (e.g. white blood cells, spleen, antibodies and thymus) which protect it from diseases and infectious agents. An associate of Louis Pasteur, Elie coined the word “phagocytosis” – to mean “the eating of cells (particularly microbial cells” by a special type of white blood cells called phagocytes. Phagocytes are specific cells of the body (e.g. white blood cells) which can surround and destroy other pathogenic cells (e.g. bacteria). Metchnikoff demonstrated in his works that certain body cells (which he called phagocytes) moved to damaged areas of the body where they eat invading bacteria. He called the process phagocytosis, and proposed the theory of cellular immunity. Though his theory that certain white blood cells could engulf and destroy harmful bodies such as bacteria where greeted by skepticism from other scientist including Louis Pasteur, Elie Metchnikoff was awarded the Nobel Prize for medicine or physiology in 1908 for his work on phagocytes. Elie formulated the basic theory on which the foundation of immunology lies, by accounting that the body is protected from infection by leukocytes that engulf bacteria and other invading organisms (a process called cellular immunity). Elie Metchnikoff is often referred as the father of immunology because of his innovative work on the immune system of higher organisms.


Paul Ehrlich (1854-1915): Systematic work on antimicrobial drugs was first initiated by the German physician Paul Ehrlich. Ehrlich worked in the fields of haematology, immunology, and chemotherapy. He coined the term “chemotherapy” and also developed the concept of “selective toxicity in the early 1900s”, which is “the ability of an agent to inhibit or kill pathogenic microorganisms without any untoward effect to the host taking it”. Paul Ehrlich tested large numbers of chemical dyes for 17 years in his quest for a “magic bullet” that would kill only microorganisms, and this led him to discover the first ever effective antimicrobial drug “Salvarsan” (a synthetic arsenic compound which was used as at the time to treat and cure syphilis). Salvarsan (the 606th chemical compound he tried) was the most successful drug for the treatment of syphilis caused by Treponema pallidum. His work in this area laid an important foundation for the era of chemotherapy – which is the use of chemicals that selectively inhibit or kill pathogens without causing damage to the victim. Ehrlich’s work further made it clear that the causative agents of many illnesses were microorganisms, and that chemicals may exist that kill the microbe, but not the patient, thus curing the illness.


Gerhard Domagk (1895-1964): Gerhard Domagk was a German pathologist and bacteriologist who reported in 1935 that prontosil (a red dye used for staining leather) was active against pathogenic Staphylococci and Streptococci in mice. It was later that the two French scientists Jacques and Therese Trefonel discovered in the same year that prontosil was broken down within the body of the host to sulphanilamide (the active component of sulpha drug) which was the true active factor that exhibited antibacterial activity against pathogenic bacteria. Domagk was credited with the discovery of Sulfonamidochrysoidine (KI-730) – the first commercially available synthetic antibiotic (which was marketed under the brand name Prontosil) for which he received the Nobel Prize for Medicine or Physiology in 1939. Sulpha drugs were the first widely used growth factor analogs shown to specifically inhibit the growth of bacteria. Gerhard Domagk’s discovery of the sulpha drugs helped to launch a second wave of research on chemotherapeutic agents – which led to the discovery of other hundreds of new antibiotics for the treatment of several infectious diseases in humans and animals.


Alexander Fleming (1881-1955): Alexander Flemming, a Scottish born physician who spent most of his time studying bacteria discovered the world’s first antibiotic “Penicillin” from the mould Penicillium notatum. Though, mankind has used a number of chemicals including herbs to treat infectious diseases since time immemorial, the astonishing discovery of penicillin (the first therapeutically used antibiotic) marked the beginning for the intensified exploration for other sources of antimicrobial agents even till date. Penicillin unlike other chemotherapeutic agents is a microbial product which can inhibit or kill susceptible microorganisms. The discovery of penicillin by Flemming opened another era for chemotherapy; and the use of antimicrobial agents to control infectious diseases. Penicillin was found to be the most effective chemotherapeutic agent against infectious diseases as at the time of its discovery before the development of resistance against the antibiotic. In 1928 Alexander Flemming streaked some plates of Staphylococcus aureus and left them to incubate until his return from a summer holiday he embarked on. In an unlikely set of circumstances, the beginning of the holiday was cold, and this allowed some contaminating mold spores (that had blown in from a nearby window) to grow up on some of Flemming’s cultured plates. The increase in temperature encouraged the growth of the S. aureus. Normally, many experimenters when confronted with a contaminated plate will eventually look for the trash bin in order to repeat their experiment, but this was not the case for Alexander Flemming, who instead, spent some time to further examine the plates. Upon examination, Flemming discovered that the fungus growing in his S. aureus plates had a zone of clearing around it where the Staphylococcus colonies would not grow. Flemming clearly guessed that the fungus was producing an antibacterial compound that had diffused into the medium, and which inhibited the growth of the S. aureus. Surprised by his findings, he cultured the fungus, a Penicillium mold, and eventually isolated a soluble extract that could kill or inhibit the growth of bacteria; and the compound was used to treat localized bacterial infections. Flemming later called the new compound penicillin after the mold from which it came. But due to limitations in the available technology as at the time, however, it was very difficult to prepare a solution that could be used throughout the body without causing problems. During World War II, the search for compounds that could fight infectious diseases increased as a result of increase in the number of wounded soldiers who died from life-threatening diseases caused by microorganisms (particularly bacteria). This led Sir Howard Florey and Ernst Chain (both from Oxford University) to start a systematic study of antimicrobial compounds with the view of developing treatments for wounded soldiers. In their search, they ran into Alexander Flemming’s report which was written 9 years earlier, and this led them to develop methods for the industrial production and purification of penicillin in England in 1941, a procedure which Flemming could not undertake as at the time he discovered penicillin – the “miracle drug”. The availability of penicillin saved countless number of wounded soldiers in World War II, and Florey and Chain, Flemming was awarded the Noble prize in Medicine and Physiology in 1945. Though there is a global threat of microbial resistance to some available drugs, the discovery of antibiotics by Sir Alexander Flemming and others has continued to positively impact medicine even till date. And the continued rise in antibiotic resistant pathogens has stepped up the search for the discovery and development of newer antimicrobial agents that will be less-amenable to microbial degradation or hydrolysis.


Sergei Winogradsky (1856-1953): Sergei Winogradsky was a Ukrainian-Russian microbiologist, ecologist and soil scientist who was among the first to delve into a different area of microbiology that involved the investigation of microbes in the environment that did not cause disease. Winogradsky pioneered the concept of bacteria (like nitrifying and purple-sulphur bacteria) that cycle nitrogen and sulphur compounds in the environment. He discovered the first known form of lithotrophy during his research with a bacterium called Beggiatoa in 1887, and reported that Beggiatoa oxidized hydrogen sulfide (H2S) as an energy source and formed intracellular sulfur droplets. Winogradsky showed in his work that certain bacteria are linked to specific biogeochemical transformations, and this provided the first example of lithotrophy, but not autotrophy. His studies on sulphur-oxidizing bacteria proposed the concept of chemolithotrphy, which is the oxidation of inorganic compounds linked to energy conservation. Sergei Winogradsky was one of the first to isolate microorganisms responsible for the conversion of elements like nitrogen and sulphur in the soil, and obtaining pure cultures of bacteria capable of oxidizing ammonia to nitrate. Winogradsky also studied the consumption of hydrogen sulfide gas by sulfur-oxidizing bacteria directly in their natural habitat. He showed that nitrifying bacteria obtained their carbon from carbondioxide (CO2), and like phototrophic organisms, that nitrifying bacteria were also autotrophs.


Martinus Beijerinck (1851-1931): Martinus Beijerinck was a Dutch microbiologist and botanists who like Sergei Winogradsky began examining the role of non-infectious microorganisms in the soil. They both reported that microorganisms play important role in nutrient recycling in the ecosystem (particularly those of nitrogen, carbon and sulphur) as well as in the process of nitrogen-fixation by symbiotic or free-living soil bacteria. Martinus Beijerinck showed in 1888 that some beneficial microbes in the soil (e.g. Rhizobium) inhabit the root of leguminous plants and provide such plants with functional nitrogen through the process of nitrogen fixation. He also discovered viruses and sulphate-reducing bacteria. Beijerinck began his work by studying the microorganisms that were present in and around plants, and he soon began experiments with microbes in the soil which led him to develop enrichment media for culturing microorganisms. Before Beijerinck’s discovery of the enrichment media, microorganisms were previously were cultivated on medium consisting of potatoes or extracts of leftover animal renderings which supported the growth of many different bacteria, with chance and population density dictating what became dominant in the culture medium. He discovered that by adding or removing certain compounds from the medium or incubating under different conditions, it was possible to favor the growth of certain microbes and prevent the growth of others. His invention of the enrichment culture enabled him to isolate many microorganisms in their pure state including Azotobacter chroococum, sulfur-reducing and sulfur-oxidizing bacteria, Lactobacillus species, and green algae. He referred to this methods as selective culture techniques – which have since then been applied to many different groups of microorganisms, allowing them to easily be brought into pure culture forms. Winogradsky and Beijerinck also provided the first evidence that viruses were infectious agents, their works in the area of soil microorganism’s which referred microorganisms as geochemical agents awaked great enthusiasm for identifying and classifying the bacteria inhabiting our natural world particularly the soil. And today, there is a branch of microbiology known as geomicrobiology which studies microorganisms that are of relevance to the geological or environmental significance.   


Frederick Griffith (1879-1941): Frederick Griffith was a British bacteriologist who performed transformation experiments that suggested that DNA was the hereditary material. His focus was on the epidemiology and pathology of bacterial pneumonia – which led him to develop the principle of bacterial transformation- which allow scientist to transform a bacterium through the introduction of exogenous DNA carrying the gene of interest. Frederick showed that streptococcus pneumonia could transform from one strain into a different strain, an effect he attributed to an unidentified transforming principle or transforming factor. In 1928, Frederick reported what is now known as Griffith’s Experiment, which was the first widely accepted demonstration of bacterial transformation. Frederick’s student, Avery Oswald, later demonstrated this principle of bacterial transformation conclusively. Frederick Griffith’s work established the foundation of molecular genetics, a field which is thriving today in the biomedical, biological and medical sciences. His work showed that DNA is the genetic material.


Avery Oswald (1877-1955): Avery Oswald was a Canadian-born American physician and medical researcher who provided the molecular explanation for Griffith’s transformation of Streptococcus pneumoniae. Avery was one of the first molecular biologists and a pioneer in immunochemistry, but he is best known for his discovery in 1944 that DNA is the material of which genes and chromosomes are made. This discovery of his was made with his co-workers Colin MacLeod and Maclyn McCarty; and the principle of bacterial transformation was actually established by the works of Avery, MacLeod and McCarty and Frederick Griffith. They showed that bacterial transformation could be carried out in the test tubes instead of the mouse that was previously used by Griffith’s in demonstrating this principle, and their painstaking experiment in deciphering this, showed that DNA was actually the transforming agent or genetic material.


Francis Crick (1916-2004): Francis Crick was an English molecular biologist, biophysicist, and neuroscientist. He co-discovered the molecular structure of the genetic material (DNA) with James Watson in 1953. Francis Crick showed in his work that genetic information flows from the DNA to RNA and then to protein; and he referred to this very important concept of molecular biology as the “central dogma” of molecular biology. Crick, Watson and Maurice Wilkins were jointly awarded the Nobel Prize on Physiology or Medicine in 1962 for their discovery of the molecular structure of the DNA. Apart from his contribution in discovering the structure of nucleic acids (e.g. DNA), Crick will be famously remembered for coming up with the idea that the genetic information of an organism actually flow between informational macromolecules in certain direction: i.e. from DNA to RNA to Protein and then to the traits expressed in the individual organism.


James Watson: Born on the 6th of April, 1928, James Watson is an American molecular biologist, geneticist, and zoologist, who is best known as a co-discoverer of the structure of deoxyribonucleic acid (DNA) in 1953. Watson co-discovered the structure of the DNA with Francis Crick (an English molecular biologist, biophysicist, and neuroscientist) in 1953. Watson and Crick both published their model of the actual structure of the DNA, and this provided a theoretical frame work for how the DNA could serve as a genetic material. There discovery of the nucleic acid (i.e. DNA as the genetic material) was very significant because it showed the basic principles underlying the mode of transmission of genetic materials from one organism to another. Three types of studies summarized the actual structure of the DNA viz: the bacteriological ones of Frederick Griffith, the biochemical ones of Oswald Avery and the structural ones of James Watson and Francis Crick; and this solidified the concept of DNA (deoxyribonucleic acid) as the genetic material of the cell. The works of these scientists led to the whole field of molecular biology and molecular genetics as well as recombinant DNA technology as a result of the collapse of the boundaries between the subjects Microbiology, Genetics and Biochemistry. The double helix of the DNA structure as we know it today was figured out by Watson and Crick; and there timely discovery set the pace for the development of the field known today as molecular biology or genetics which have tremendously impacted and revolutionized the practice of medicine and biomedical sciences. The 1962 Nobel Prize in Physiology or Medicine was awarded to Watson and Crick because of their discovery of the molecular structure of the DNA.


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