Klebsiella pneumoniae is a Gram-negative rod-shaped bacteria of the genus Klebsiella and the family Enterobacteriaceae. They are members of the normal intestinal flora of humans and animals and may be isolated from a variety of environmental sources.
K. pneumoniae was first isolated in the late 19th century and was initially known as Friedlander’s bacterium. Classic cases of pneumonia, characterized by production of brick-red or “currant jelly” sputum, were known to be caused by Friedlander’s bacillus (Klebsiella pneumoniae).
General Properties of Klebsiella pneumoniae
Gram – negative
- Non-spore-forming rods
- Facultative anaerobes
- Catalase Test: Positive
- Oxidase Test: Negative
- Lactose fermenter (forms pink-colored colonies on MacConkey Agar).
- Presence of polysaccharide capsule (in the culture plate mucoid colonies are seen).
- Non-motile (Klebsiella species are nonmotile and non-flagellated and thus have no H antigens).
Virulence Factors of K. pneumoniae
Virulence factors of Klebsiella pneumoniae will be discussed in-depth in another post.
Laboratory diagnosis of K. pneumoniae infection
Sample: Sputum (Red currant-jelly sputum may be seen in a patient infected with K.pneumoniae), mid-stream urine, or blood (depending on the suspected illness/clinical presentation).
Colony characteristics of Klebsiella pneumoniae
- Blood Agar: Mucoid, non-hemolytic colonies
- MacConkey Agar: Mucoid, lactose-fermenting (pink colored) colonies
Various biochemical tests using conventional methods or miniature commercial system (API-20E or E
|Indole Production Test||Negative (K.oxytoca is indole positive)|
|Citrate Utilization Test||Positive|
|Hydrogen Sulfide (H2S) Production||Negative|
|TSI test||Acid/Acid, Gas (++), No H2S|
|Urea Hydrolysis Test||Positive|
|Lysine Decarboxylase Test||Positive|
|Arginine Dihydrolase Test||Negative|
|Ornithine decarboxylase test||Negative|
|Motility at 36 °C||Non-motile|
|Acetate Utilization Test||Positive|
Note: To minimize the cost and effort, some diagnostic/hospital laboratories perform only certain tests such as Triple Sugar Iron Agar (TSI), sulfite indole motility (SIM) / urease indole motility (UIM), and citrate utilization test to identify isolates of Enterobacteriaceae family, full panel/commercially available miniature test system (API-20E and Enterotube test) is used only when the test results are inconclusive.