Citrobacter koseri: Introduction, Identification Features, and Keynotes

Introduction of Citrobacter koseri

Citrobacter koseri is previously known as Citrobacter diversus. It is a facultative anaerobe of 1.0 × 2.0–6.0 μm in size, motile, non-capsulated, and gram-negative bacillus of the family Enterobacteriaceae. Citrobacter koseri acts as etiological agents of various pathological conditions like urinary tract infections (UTIs), pneumonia, bacteremia, and neonatal meningitis.

Citrobacter koseri growth on CLED agar
Fig. Citrobacter koseri growth on CLED agar

Biochemical Reactions of Citrobacter koseri

Basic FeaturesProperties
1. Gram StainingGram-Negative Rods (GNRs)
2. SporeNon-Sporing
3. CapsuleNegative
4. MotilityMotile
5. PigmentNegative
6. Growth in potassium cyanide (KCN) mediumPositive
7. Catalase testPositive
8. Oxidase testNegative
9. Nitrate reduction testPositive
10. MR (Methyl Red) testPositive
11. VP (Voges- Proskauer) assayNegative
12. OF (Oxidative-Fermentative) testFermentative/Facultative Anaerobes
13. GasPositive
14. H2S productionNegative
15. Indole formationPositive
16. Urease/ urea hydrolysis testVariable
17. Citrate/ citrate utilizationPositive 
18. DNase testNegative
19. Glucose fermentationPositive 
20. Maltose fermentationPositive 
21. Lactose fermentationPositive 
22. Sucrose fermentationPositive
23. Xylose fermentationPositive
24. Mannitol fermentationPositive
25. Acetate UtilizationPositive
26. ONPG (β-galactosidase)Positive
27. Phenylalanine Deaminase (PDA)/PPA TestNegative
28. Lipase testNegative
29. Esculin Hydrolysis testNegative
30. Lysine Decarboxylase TestNegative
31. Ornithine Decarboxylase TestNegative
32. Arginine Dihydrolase TestVariable
Table: Properties of Citrobacter koseri

Keynotes on Citrobacter

  • Citrobacter koseri is indole positive while Citrobacter freundii is negative.
  • Citrobacter species are found in soil and water, and in the human intestines.
  • Citrobacter are motile due to having peritrichous flagella.
  • Clinically important Citrobacter species are C. freundii, C. koseri, and C. braakii.
  • Other species of Citrobacter are C. amalonaticus, C. farmeri, C. youngae, C. werkmanii, C. sedlakii,C. rodentium, C. gillenii, and C. murliniae.
  • C. freundii is more resistant than C. koseri to most antibiotics.

Further Readings

  • Cowan and Steel’s, manual for the identification of medical bacteria
  • Topley and Wilson microbiology and microbial infection Topley and Wilson’s microbiology and microbial infection – Bacteriology-2-10th Edn.
  • Manual of Clinical Microbiology   -Patrick R. Murray -8th Edn.
  • Bailey and Scott’s  Diagnostic Microbiology -13th Edn.
  •  Mackie & Mc Cartney  Practical Medical Microbiology- 14th  Edn.
  • Diagnostic Microbiology -Connie R. Mahon & George Manuselis
  • Koneman Color Atlas and Textbook of Diagnostic Microbiology-6th  Edn.
  • Jawetz Melnick and Adelberg’s Medical Microbiology- 25th Edn.
  • Lippincott’s –Illustrated- review-Microbiology-3rd Edn.
  •  Mandell’s Infectious Disease-7th Edn.
  • Bergey’s Manual of Systemic Bacteriology – 2nd  Edn.
  • Text Book of Microbiology -Anantanarayan & Paniker-9th Edn.

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