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.

Biochemical Reactions of Citrobacter koseri

Basic Features	Properties
1. Gram Staining	Gram-Negative Rods (GNRs)
2. Spore	Non-Sporing
3. Capsule	Negative
4. Motility	Motile
5. Pigment	Negative
6. Growth in potassium cyanide (KCN) medium	Positive
7. Catalase test	Positive
8. Oxidase test	Negative
9. Nitrate reduction test	Positive
10. MR (Methyl Red) test	Positive
11. VP (Voges- Proskauer) assay	Negative
12. OF (Oxidative-Fermentative) test	Fermentative/Facultative Anaerobes
13. Gas	Positive
14. H2S production	Negative
15. Indole formation	Positive
16. Urease/ urea hydrolysis test	Variable
17. Citrate/ citrate utilization	Positive
18. DNase test	Negative
19. Glucose fermentation	Positive
20. Maltose fermentation	Positive
21. Lactose fermentation	Positive
22. Sucrose fermentation	Positive
23. Xylose fermentation	Positive
24. Mannitol fermentation	Positive
25. Acetate Utilization	Positive
26. ONPG (β-galactosidase)	Positive
27. Phenylalanine Deaminase (PDA)/PPA Test	Negative
28. Lipase test	Negative
29. Esculin Hydrolysis test	Negative
30. Lysine Decarboxylase Test	Negative
31. Ornithine Decarboxylase Test	Negative
32. Arginine Dihydrolase Test	Variable

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.
• http://www.antimicrobe.org/b93.asp
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5054941/#