Biochemical Characterization of Citrobacter diversus (Burkey) Werkman and Gillen and Designation of the Neotype Strain

This study characterized 137 strains of Citrobacter diversus collected at the Centers for Disease Control between 1962 and 1970. The authors determined biochemical properties of these bacteria, which are gram-negative, rod-shaped members of the Enterobacteriaceae family. C. diversus strains consistently produced indole and ornithine decarboxylase enzymes, fermented the sugar adonitol, and failed to grow in potassium cyanide (KCN) medium. Notably, these bacteria did not produce detectable hydrogen sulfide in triple sugar-iron agar medium under standard incubation conditions, though some strains produced it in peptone-iron agar. The authors designated strain 3613-63 (ATCC 27156) as the neotype reference strain for the species. Comparison tables were provided to differentiate C. diversus from related species including hydrogen sulfide-positive and hydrogen sulfide-negative forms of C. freundii and Enterobacter cloacae. The authors established C. diversus as the second accepted species of the genus Citrobacter, reviving a name originally proposed by Werkman and Gillen in 1932.

Key findings

• C. diversus is characterized by indole production, ornithine decarboxylase activity, adonitol fermentation, and failure to grow in KCN medium
• Unlike C. freundii, C. diversus does not produce hydrogen sulfide in triple sugar-iron agar under standard incubation conditions
• Strain 3613-63 (ATCC 27156) was designated as the neotype strain for C. diversus
• C. diversus can be differentiated from C. freundii and E. cloacae using specific biochemical tests, particularly adonitol fermentation and KCN growth inhibition
• The species designation revived the validly published name C. diversus from 1932, which has priority over later proposed names like Citrobacter koseri and Levinea malonatica