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).
Klebsiella
Klebsiella
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
- Capsule
- Cell wall receptors
- Lipopolysaccharide (endotoxin)
- Fimbriae
- Siderophores
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
Test Name | Results |
Catalase test | Positive |
Oxidase test | Negative |
Indole Production Test | Negative (K.oxytoca is indole positive) |
Methyl-Red Test | Negative |
Voges-Proskauer Test | 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 |
D-Glucose (acid/gas) | Positive/Positive |
D-mannitol fermentation | Positive |
Sucrose fermentation | Positive |
Lactose fermentation | Positive |
D-sorbitol fermentation | Positive |
Cellobiose | Positive |
Esculin hydrolysis | Positive |
Acetate Utilization Test | Positive |
ONPG 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.
What about the pressure resistance of klebsiella ?