The speciesC. amalonaticus, C. koseri, and C. freundii can use citrate as a sole carbon source. Citrobacter species are differentiated by their ability to convert tryptophan to indole (C. koseri is the only citrobacter to be commonly indole-positive), ferment lactose (C. koseri is a lactose fermentor), and use malonate.[3]
Citrobacter shows the ability to accumulate uranium by building phosphate complexes.[4]
Citrobacter freundii strains have inducible ampC genes encoding resistance to ampicillin and first-generation cephalosporins.[8] In addition, isolates of Citrobacter may be resistant to many other antibiotics as a result of plasmid-encoded resistance genes.[7]
^Lipsky, Benjamin A.; Hook III, Edward W.; Smith, Arlene A.; Plorde, James J. (1980). "Citrobacter Infections in Humans: Experience at the Seattle Veterans Administration Medical Center and a Review of the Literature". Clinical Infectious Diseases. 2 (5): 746–760. doi:10.1093/clinids/2.5.746. ISSN1058-4838. PMID6763304.
^Macaskie, Lynne E.; Empson, Ruth M.; Cheetham, Anthony K.; Grey, Clare P.; Skarnulis, A. Jerome (1992). "Uranium bioaccumulation by a Citrobacter sp. as a result of enzymically mediated growth of polycrystalline HUO2PO4". Science. 257 (5071): 782–784. Bibcode:1992Sci...257..782M. doi:10.1126/science.1496397. ISSN0036-8075. PMID1496397.