Written by MicroDok

Klebsiella pneumoniae is a Gram-negative, encapsulated, lactose-fermenting, non-motile, facultative rod in the genus Klebsiella and family Enterobacteriaceae. In addition to O and H antigens, K. pneumoniae possess K antigens (that consists mainly of polysaccharides). K antigens are capsular antigens found mostly amongst members of the Enterobacteriaceae family; and in the case of K. pneumoniae, the K antigens are usually external to the somatic antigens (O and H) of the pathogen. K. pneumoniae is a less common pathogen of the intestinal tract of humans and animals than E. coli. K. pneumoniae is notorious in causing bloodstream infections and severe pneumonia in humans. However, Klebsiella species are most commonly found in the soil and water, and some are nitrogen (N2)-fixing bacteria. K. pneumoniae is a well-studied N2-fixing bacterium that is free-living and exists as a chemoorganotroph in the soil. Generally, K. pneumoniae is mostly implicated as the main causative agent of nosocomial- and community-acquired pneumonia and some UTI.       


K. pneumoniae causes opportunistic infections in humans. Persons with history of type I diabetes (i.e. diabetes mellitus), alcoholism, respiratory infections and malnutrition are most often affected. The elderly and individuals with weakened immunity are also prone to K. pneumoniae infections. The human colon and respiratory tract are the main reservoir of K. pneumoniae in the body. Some healthy people harbour K. pneumoniae in their respiratory tract and may be prone to a pneumonia anytime their immunity becomes compromised or is weakened. The pathogenesis of K. pneumoniae is enhanced by its large polysaccharide capsules and its ability to produce toxins and other extracellular factors as is typical to members of the Enterobacteriaceae family.

The capsule produced by K. pneumoniae obstructs phagocytosis in the host while the endotoxin causes inflammation, fever and septic shock. K. pneumoniae reaches the lungs where it produces pneumonia (different from that caused by Streptococcus pneumoniae) via inhalation of respiratory droplets from the upper respiratory tract of individuals harbouring the pathogen. A thick, bloody sputum known as currant-jelly sputum is the main clinical symptom presented in individuals whose pneumonia is caused by K. pneumoniae. Aside pneumonia and UTI, bacteraemia and sepsis are other clinical episodes associated with an infection with K. pneumoniae. Feacal contamination of catheters can result to a UTI, an invasion of IV lines and/or bowel defects in individuals with weakened immune system may result in sepsis.


Microscopy, isolation and identification of the pathogen is often the mainstay of diagnosing any infection in which K. pneumoniae is implicated or suspected. K. pneumoniae is Gram-negative and non-motile. Characteristically, K. pneumoniae produces mucoid colonies on growth media. K. pneumoniae grows on differential media including MacConkey agar producing mucoid colonies and CLED (producing yellow-mucoid colonies). On blood agar, K. pneumoniae produces large grey or pale mucoid colonies. Biochemically, K. pneumoniae is urease positive, lactose-fermenting and citrate positive. It is also positive to malonate utilization test and lysine decarboxylase (LDC) test. Some species of Klebsiella (e.g. K. oxytoca) is indole positive.

Illustration of the mucoid and slimy nature of Klebsiella on growth media


The treatment of K. pneumoniae infection should be guided by a proper susceptibility test result owing to the nature of the pathogen to produce extracellular substances including beta-lactamases that render antimicrobial agents directed towards it ineffective. Some strains of Klebsiella especially those associated with hospital-acquired infections are multidrug resistant; and thus, the treatment of K. pneumoniae infection should be embarked using multiple antibiotic regimens. Third-generation cephalosporins and aminoglycosides are often used for the treatment of both nosocomial and community-acquired K. pneumoniae infections.


The control of K. pneumoniae infection in the community and around hospital settings depends on ensuring proper infection control strategies when handling patients and using invasive and non-invasive medical devices (e.g. catheters, respirators and IV lines). These medical devices known to spread the pathogen should be used cautiously and only when needed.


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