Klebsiella pneumoniae: Introduction,Morphology, Culture Characteristics, Pathogenecity, Lab Diagnosis and Treatment

Glucose utilization test of Klebsiella pneumoniae

Introduction of Klebsiella pneumoniae 

Klebsiella pneumoniae gucose utilization test using Andrade’s indicator as shown above image. Klebsiella pneumoniae consists of Gram-negative, capsulated, non-sporing, non-motile bacilli that grow well on an ordinary medium( nutrient agar). They produce pink mucoid colonies on MacConkey agar. They are widely distributed in nature, occurring as commensals in human and animal intestines and also saprophytes in soil.

Scientific Classification of Klebsiella pneumoniae

Domain: Bacteria

Phylum: Proteobacteria

Class: Gammaproteobacteria

Order: Enterobacterales

Family: Enterobacteriaceae

Genus: Klebsiella

Species: K. pneumoniae

The classification of Klebsiella has been undergone various modifications. They have been classified into two species and they are Klebsiella pneumoniae and Klebsiella oxytoca. Klebsiella pneumoniae is further subdivided into four subspecies ( subsp.) and they are-

      1. Klebsiella pneumoniae subsp. aerogenes
      2. Klebsiella pneumoniae subsp. pneumoniae
      3.  Klebsiella pneumoniae subsp. ozaenae
      4. Klebsiella pneumoniae subsp. rhinoscleromatis

Note: Unlike other subsp. , Klebsiella oxytoca is indole positive.


Morphology of Klebsiella pneumoniae

They are short, plump, Gram-negative, encapsulated, non-motile rods. They are about 1-2 um x 0.5-0.8 um.

Culture Characteristics

Klebsiellae grows well on ordinary media to an optimal temperature of 37°C in 18-24 hours. The colonies appear large, mucoid, and pink to red in color on MacConkey agar. On nutrient agar,  colonies appear large, mucoid, and white in color as shown above picture. The mucoid nature of colonies is due to the presence of capsular material produced by the organism.

Biochemical  Reactions

They ferment sugars like glucose, lactose, sucrose, mannitol with the production of acid and gas. They are urease positive, indole negative, MR negative, VP positive, and citrate positive( IMViC–++).  These are typical reactions of Klebsiella pneumoniae subsp. aerogenes.

Antigenic Structure

There are two types of antigenic structures and they are-

Capsular (K) antigen: On the basis of capsular antigen, the klebsiellae have been classified into 80 serotypes. Serotypes 1-6 are found most frequently in human respiratory tract infections.

Somatic(O) antigen: They contain five different somatic antigens and they are O1, O2, 03,04, and 05.

Pathogenicity of Klebsiella

Even though as normal flora of intestines, Klebsiella may cause infections mostly in people with a weakened immune system. Klebsiella pneumoniae subsp. aerogenes is the most populous member next to E. coli of aerobic bacterial flora of our intestine. It is responsible for-

  • severe bronchopneumonia
  • urinary tract infections (UTIs)
  • nosocomial infections
  • wound infections
  • septicemia
  • meningitis and rarely
  • diarrhea.

Pneumonia due to Klebsiella is a serious disease with high case fatality. Positive blood cultures can be obtained in about 25% of cases of pneumonia. It is a very important hospital-acquired infection of the lower respiratory tract. Some strains of K. pneumoniae isolated from cases of diarrhea produce an enterotoxin similar to the heat-stable toxin of E.coli.

Klebsiella pneumoniae subsp. ozaenae is responsible for atrophic rhinitis, a condition known as ozaena.

Klebsiella pneumoniae subsp. rhinoscleromatis causes a granulomatous disease of the nose and pharynx called rhinoscleroma.

Mode of Transmission 

Bacteria spread through exposure to the respiratory tract which causes pneumonia.

  • Enters the blood to cause an infection in the bloodstream.
  • Most well-known in hospitals spread through person-to-person contact by contaminated hands of surrounded people in the hospitals, whether it be an employee or a patient.
  • Klebsiella is spread very easily and rapidly, but not through the air.
  • Healthcare settings are most vulnerable to Klebsiella infections due to the nature of procedures that allow easy access of bacteria into the body. Patients who are on ventilators, catheters, or surgery wounds are highly prone to catching this deadly infection.


The symptoms of a K. pneumoniae infection differ depending on where the infection is located, and are similar to symptoms of the same diseases caused by other microbes. For instance, meningitis from K. pneumoniae produces the hallmark symptoms of bacterial meningitis, including fever, confusion, neck stiffness, and sensitivity to bright lights. Bloodstream infections (bacteremia and sepsis) from Klebsiella cause fever, chills, rash, light-headedness, and altered mental states. Pneumonia from K. pneumoniae can result in 1) Fevers and chills 2) Flu-like symptoms 3)Cough, which may produce mucus that’s yellow, green, or bloody 4) breathing issues.

Laboratory Diagnosis of Klebsiella pneumoniae

Specimen: Sputum, urine, blood,  pus, CSF
Gram stain: Gram-negative rods
Capsule visualization: Gram Stain of Sputum Specimen Showing Capsules Surrounding a Gram-Negative Bacillus
Culture: On MacConkey agar – mucoid red/pink colonies
On EMB –Klebsiella species produces large, mucoid, pink to purple colonies with no metallic green sheen on EMB agar.
On CLED AGAR – This medium supports the growth of urinary pathogens and provides distinct colony morphology. Klebsiella pneumoniae on CLED Agar. Large, mucoid colonies. Bromothymol blue indicator in the agar changes to yellow due to acidification of the medium due to lactose fermentation by bacterial growth. Lactose fermenters appear yellow. Non Lactose fermenters remain a translucent blue.
 String test: A colony that stretches more than 5 mm using a standard inoculation loop tests positive for hypermucoviscosity. Mucoid colony of Klebsiella pneumoniae. When colonies were touched with a loop and the loop lifted vertically from the surface of the agar plate, mucoid isolates adhered to the loop as it was lifted from the plate.
 India ink capsule stain: India Ink Capsule Stain of Klebsiella pneumoniae showing white capsules (Glycocalyx) surrounding purple cells -The background will be dark. -The bacterial cells will be stained purple. -The capsule (if present) will appear clear against the dark background.

 Klebsiella API20E : oxidase -ve indol –ve H2S –ve citrate +ve

 Treatment of Klebsiella pneumoniae

Klebsiella infections that are not drug-resistant can be treated with antibiotics. Infections caused by KPC-producing bacteria can be difficult to treat because fewer antibiotics are effective against them. In such cases, a microbiology laboratory must run tests to determine which antibiotics will treat the infection These drugs include aminoglycosides, polymyxins, tigecycline, fosfomycin, temocillin.

Further Readings

  1. Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
  2. Clinical Microbiology Procedure Handbook Vol. I & II, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
  3. Colour Atlas and Textbook of Diagnostic Microbiology. Editors: Koneman E.W., Allen D.D., Dowell V.R. Jr and Sommers H.M.
  4. Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
  5. Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
  6.  Manual of Clinical Microbiology. Editors: P.R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover and R. H. Yolken, 7th ed 2005, Publisher ASM, USA
  7.  Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.
  8. Topley & Wilsons Principle of Bacteriology, Virology and immunology Vol I, II, III, IV & V. Editors: M.T. Parker & L.H. Collier, 8th ed 1990, Publisher Edward Arnold publication, London.
  9. Medical Microbiology-The Practice of Medical Microbiology Vol-2-12th Edn. –Robert Cruickshank
  10. District Laboratory Practice in  Tropical Countries  –  Part-2-   Monica Cheesebrough-   2nd Edn Update
  11. https://www.cdc.gov/hai/organisms/klebsiella/klebsiella.html
  12. https://www.webmd.com/a-to-z-guides/klebsiella-pneumoniae-infection
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