C. amalonaticus was found responsible of enteric fever-like illness (one report).
Citrobacter freundii is often found in clinical specimens as an opportunistic or secondary pathogen.
Citrobacter rodentium is the causative agent of Transmissible Murine Colonic Hyperplasia.
Citrobacter cronae was isolated from rectal swabs or stool samples of immunocompromised patients.
Citrobacter europaeus was isolated from human faeces and well water.
Citrobacter pasteurii was isolated from human diarrhoea.
Citrobacter telavivensis was isolated from a human rectal sample.
Citrobacter braakii Gram-staining
Citrobacter braakii colonies on Sheep Blood Agar
 
Catalase
Ornithine
decarboxylase
Citrate
utilization
Malonate
utilization
Indole
production
Melibiose
fermentation
Dulcitol
fermentation
D-adonitol
fermentation
C. amalonaticus
+
+
+
-
+
-
-
-
C. freundii
+
-
[+]
[-]
[-]
+
[-]
-
C. braakii
+
+
[+]
-
[-]
[+]
d
-
C. cronae
+
d
d
[+]
-
-
nd
d
C. europaeus
+
+
-
nd
-
+
+
-
C. farmeri
+
+
-
-
+
+
-
-
C. gillenii
+
-
[-]
+
-
d
-
-
C. koseri (C. diversus)
+
+
+
+
+
-
d
+
C. murliniae
-
-
+
-
+
d
+
-
C. pasteurii
-
-
+
-
-
-
d
-
C. portucalensis
-
-
+
 
-
+
-
-
C. rodentium
+
+
-
+
-
-
-
-
C. sedlakii
+
+
[+]
+
[+]
d
+
-
C. telavivensis
+
nd
+
 
+
+
-
-
C. werkmanii
[+]
-
+
+
-
-
-
-
C. youngae
[+]
-
[+]
-
[-]
-
[+]
-
Genus Citrobacter
Taxonomy
Morphology
Cultural characteristics
Biochemical characters
Ecology
Pathogenicity
References
Phylum Proteobacteria, Class Gammaproteobacteria, Order Enterobacterales, Family Enterobacteriaceae, Genus Citrobacter,
- Citrobacter amalonaticus (Young et al. 1971) Brenner and Farmer 1982, synonym: Levinea amalonatica;
- Citrobacter braakii  Brenner et al. 1993, synonym: Citrobacter genomospecies 6;
-
Citrobacter cronae Oberhettinger et al. 2020;
- Citrobacter diversus (Burkey 1928) Werkman and Gillen 1932, (actually C. koseri);
-
Citrobacter europaeus Ribeiro et al. 2017;
- Citrobacter farmeri Brenner et al. 1993 (Citrobacter amalonaticus biovar 1, Citrobacter genomospecies 4),
- Citrobacter freundii
(Braak 1928) Werkman and Gillen 1932 - type species, synonyms: Bacterium freundii, Escherichia freundii;
- Citrobacter gillenii
Brenner et al. 2000, synonym: Citrobacter genomospecies 10,
- Citrobacter koseri Frederiksen 1970, synonyms: C. diversum, C. diversus, Aerobacter diversum, Levinea malonatica;
- Citrobacter murliniae Brenner et al. 2000, synonym: Citrobacter genomospecies 11;
- Citrobacter pasteurii Clermont et al. 2015;
-
Citrobacter portucalensis Ribeiro et al. 2017;
- Citrobacter rodentium Schauer et al. 1996, synonyms: C. freundii biovar 4280, Citrobacter genomospecies 9;
- Citrobacter sedlakii Brenner et al. 1993, synonym: Citrobacter genomospecies 8;
-
Citrobacter telavivensis corrig. Ribeiro et al. 2021;
- Citrobacter werkmanii Brenner et al. 1993, synonym: Citrobacter genomospecies 7;
- Citrobacter youngae Brenner et al. 1993, synonym: Citrobacter genomospecies 5.
Gram-negative, straight rods, 1.0 x 2.0-6.0 μm, found singly or in pairs. Frequently
motile by means of peritrichous flagella. Usually not encapsulated.
Colonies on nutrient agar are generally 2-4 mm in diameter, smooth, low convex,
moist, translucent or opaque, and gray with a shiny surface and entire edge. Mucoid
or rough forms may occur.
Facultatively anaerobic. Incubation temperature 37 °C.
Media: Trypticase Soy Agar with 5% sheep blood, Nutritive Agar. Grows on media that
inhibit
Escherichia coli: Muller’s tetrathionate broth, Leifson’s selenite broth, Wilson-
Blair  bismuth sulfite, Kristensen briliant green-phenol red agar.
Isolated from soil, water, seawage, food, feces, urine, clinical samples (humans
and other animals including mammals, birds, reptiles and amphibians).
They seem to be normal intestinal inhabitants but may occur in sporadic and mass
alimentary infections or some urinary tract infections, respiratory tract infections,
wound infections, osteomyelitis, meningitis and brain abscesses (young organisms
are more sensitive), enteritis, and septicemia.
O, K and H antigens are presented. Cross-reactions are identified with antisera of the
other members of the Enterobacteriaceae (Salmonella, Escherichia).
  1. J. G. Holt et al., 1994. Facultatively Anaerobic Gram-Negative Rods. Subgroup 1. Family Enterobacteriaceae. In: Begey’s Manual of
    Determinative Bacteriology, 9th-edition, Williams & Wilkins, pp 175-189.
  2. Don J. Brenner and J.J. Farmer III, 2001. Family I. Enterobacteriaceae. In: Bergey’s Manual of Systematic Bacteriology, Second
    edition, Vol two, part B, George M. Garrity (Editor-in-Chief), pp 587-897.
  3. Werkman (C.H.) and Gillen (G.F.): Bacteria producing trimethylene glycol. Journal of Bacteriology,1932, 23,167-182
  4. Ewing(W.H.) and Davis (B.R.): Biochemical characterization of Citrobacter diversus (Burkey) Werkman and Gillen and designation
    of the neotype strain. Int. J. Syst. Bacteriol., 1972, 22, 12-18.
  5. Validation list 8. Int. J. Syst. Bacteriol., 1982, 32, 266-268. [FARMER III (J.J.): The genus Citrobacter.
  6. M.P. STARR et al. (ed.), The procaryotes, a handbook on habitats, isolation, and identification of bacteria.Springer-Verlag, Berlin,
    1981, p. 1140-1147
  7. Abbot SL, Klebsiella, Enterobacter, Citrobacter, Serratia, Plesiomonas, and other Enterobacteriaceae. In: Murray PR, Baron EJ,
    Jorgensen JH, Pfaller MA, Yolken RH. Manual of clinical microbiology. 8th edition. Washington DC: American Society for
    Microbiology, 2003:684-700
  8. Don J. Brenner. Biochemical Identification of citrobacter Species Defined by DNA Hybridization and Description of Citrobacter
    gillenii sp. nov. (formerly C. genomospecies 10) and C. murliniae sp. nov. (formerly Citrobacter genomospecies 11), Journal of
    Clinical Microbiology Aug. 1999, p. 2619–2624, Vol. 37, No. 8.
  9. Adeolu M, Alnajar S, Naushad S, S Gupta R. Genome-based phylogeny and taxonomy of the 'Enterobacteriales': proposal for
    Enterobacterales ord. nov. divided into the families Enterobacteriaceae, Erwiniaceae fam. nov., Pectobacteriaceae fam. nov.,
    Yersiniaceae fam. nov., Hafniaceae fam. nov., Morganellaceae fam. nov., and Budviciaceae fam. nov. Int J Syst Evol Microbiol
    2016; 66:5575-5599.
  10. Oberhettinger P, Schule L, Marschal M, Bezdan D, Ossowski S, Dorfel D, Vogel W, Rossen JW, Willmann M, Peter S. Description
    of Citrobacter cronae sp. nov., isolated from human rectal swabs and stool samples. Int J Syst Evol Microbiol 2020; 70:2998-3003.
  11. Ribeiro TG, Clermont D, Branquinho R, Machado E, Peixe L, Brisse S. Citrobacter europaeus sp. nov., isolated from water and
    human faecal samples. Int J Syst Evol Microbiol 2017; 67:170-173.
  12. Clermont D, Motreff L, Passet V, Fernandez JC, Bizet C, Brisse S. Multilocus sequence analysis of the genus Citrobacter and
    description of Citrobacter pasteurii sp. nov. Int J Syst Evol Microbiol 2015; 65:1486-1490.
  13. Ribeiro TG, Goncalves BR, da Silva MS, Novais A, Machado E, Carrico JA, Peixe L. Citrobacter portucalensis sp. nov., isolated from
    an aquatic sample. Int J Syst Evol Microbiol 2017; 67:3513-3517.
  14. Ribeiro TG, Izdebski R, Urbanowicz P, Carmeli Y, Gniadkowski M, Peixe L. Citrobacter telavivum sp. nov. with chromosomal mcr-9
    from hospitalized patients. Eur J Clin Microbiol Infect Dis 2021; 40:123-131.
Positive results for catalase (most strains), methyl red, ONPG (most strains), nitrate
reduction, mucate (most strains), Tartrate (Jordans), acid production from: glucose
(with gas), L-arabinose, maltose, L-rhamnose, trehalose, D-xylose, D-mannitol,
mannose and D-sorbitol.

Negative results fo oxidase, lysine decarboxylase, Voges-Proskauer, phenilalanine,
gelatinase, esculin hydrolysis (most of strains), deoxyribonuclease, lipase, acid
production from: erythritol and myo-inositol.
(c) Costin Stoica
Antibiogram
Encyclopedia
Culture media
Biochemical tests
Stainings
Images
Movies
Articles
Identification
Software
R E G N U M
PROKARYOTAE
Differential characters between species:
Legend: +  positive 90-100%, - negative 90-100%, [+] positive 75-89%,
[-] negative 75-89%, d positive 25-74%, nd not determined.
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