Klebsiella pneumoniae: Properties, Diseases, Lab Diagnosis

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 pneumoniae causes infections in people of all age groups, especially in infants, the elderly, immunocompromised, and alcoholics. It is one of the leading causes of hospital-acquired (nosocomial) infections. The range of infections includes pneumonia (it is a frequent cause of ventilator-associated pneumonia), urinary tract infection, bloodstream infection (BSI), and liver abscesses. Though Klebsiella pneumoniae accounts for a small percentage of pneumonia cases, the case fatality rates are high (up to 90% in untreated cases).

Klebsiella pneumoniae is a major threat to public health with the emergence of multidrug-resistant strains, rendering infection by these strains very challenging to treat. Strains of K. pneumoniae producing extended-spectrum beta-lactamases (ESBLs) or carbapenemases are considered global priority pathogens.

General Properties of Klebsiella pneumoniae

Mucoid colonies of Klebsiella pneumoniae
mucoid colonies
  1. Gramnegative
  2. Non-spore-forming rods
  3. Facultative anaerobes
  4. Catalase Test: Positive
  5. Oxidase Test: Negative
  6. Lactose fermenter (forms pink-colored colonies on MacConkey Agar).
  7. Presence of polysaccharide capsule (in the culture plate mucoid colonies are seen).
  8. 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.

Virulence factors of K. pneumoniae (Source)

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 Enterotube test) is done to identify the suspected colony as Klebsiella pneumoniae.  Some of the commonly used tests for the identification of Klebsiella pneumoniae are given below.

Test Name Results
Catalase testPositive
Oxidase testNegative
Indole Production TestNegative (K.oxytoca is indole positive)
Methyl-Red Test Negative
Voges-Proskauer Test Positive
Citrate Utilization Test Positive
Hydrogen Sulfide (H2S) ProductionNegative
TSI testAcid/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.


  1. Bailey & Scott’s Diagnostic Microbiology, Forbes, 11th edition
  2. Ashurst JV, Dawson A. Klebsiella Pneumonia. [Updated 2023 Jul 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519004/ 
  3. Qu, T. T., Zhou, J. C., Jiang, Y., Shi, K. R., Li, B., Shen, P., Wei, Z. Q., & Yu, Y. S. (2015). Clinical and microbiological characteristics of Klebsiella pneumoniae liver abscess in East China. BMC infectious diseases, 15, 161. https://doi.org/10.1186/s12879-015-0899-7
  4. Madigan Michael T, Bender, Kelly S, Buckley, Daniel H, Sattley, W. Matthew, & Stahl, David A. (2018). Brock Biology of Microorganisms (15th Edition). Pearson.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

2 thoughts on “Klebsiella pneumoniae: Properties, Diseases, Lab Diagnosis

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