Citrobacter freundii: Introduction, Identification Features, and keynotes

Introduction of Citrobacter freundii

Citrobacter freundii is a member of the family, Enterobacteriaceae and it is a Gram-negative bacillus, non-sporing, non-encapsulated, aerobic, or facultative anaerobe that causes various types of infections of the urinary tract, respiratory tract, peritoneum, liver, bone, endocardium, intestines, soft tissue, meninges, and the bloodstream. It’s also the causative agent of other diseases, including biliary, hepatic, and pancreatic diseases.

Biochemical Reactions of Citrobacter freundii

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 productionPositive
15. Indole formationNegative
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 freundii

Keynotes on Citrobacter

  • Citrobacter freundii is H2S positive and indole negative.
  • Citrobacter koseri is H2S negative and indole positive.
  • Citrobacter freundii is often the cause of significant opportunistic infections.
  • Medically important species of Citrobcater are C. freundii and C. koseri. C. koseri is responsible for neonatal meningitis and brain abscess while C. freundii is a causative agent of gastroenteritis, neonatal meningitis, and septicemia.

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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