Genus Citrobacter

Bacteria of the genus Citrobacter from the family Enterobacteriaceae are inhabitants of the intestinal tract and are present in sewage, surface waters, and food contaminated with fecal material. In accordance with close phylogenetic relationship to Salmonella, Citrobacter has a so-called Salmonella-type enterobacterial LPS core (inner Hep3Kdo2 pentasaccharide with both HepI and HepII phosphorylated at 0-4 and HepII substituted at 0-3 with a Glc residue). Two core structures recently fully characterized (C. werkmanii PCM 1548 and PCM 1549) (Kondakova et al., 2009) also contain a GalA residue linked at position 7 of HepIII, which is known to occur in both Salmonella-type (Providencia, see below) and non-Salmonella-type core (Proteus, Holst, 2002, 2007). 

Kondakova, A.N., Vinogradov, E., Katzenellenbogen, E., Kocharova, N.A., Lindner, B., Knirel, Y.A. Structural studies on the lipopoly saccharide core of bacteria of the genus Citrobacter two different core structures in Citrobacter 014 serogroup. J Carbohydr Chem 28 (2009) 298-315. 

Today the genus Citrobacter together with the genera Escherichia, Shigella Salmonella and Yersinia is included as an independent genus in the tribe Escherichieae of the Enterobacteriaceae family [5]. 

Table 2. Biochemical differential diagnosis between genus Citrobacter and related senera... 

A complete and valid comparative immunochemical analysis of lipopoly-saccharides of a genus or species can be carried out only if a serological classification of the respective genus is available. Such a classification exists [13] for Salmonella, E. coli, Shigella, and recently for Citrobacter [36, 88], and immunochemical studies on their O antigens have been performed in the last decades [74]. 

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