Edwardsiella tarda is occasionally isolated in stool specimens and can biochemically be confused with which organism?

• A. Salmonella
• B. Enterohemorrhagic E. coli
• C. Vibrio cholerae
• D. Yersinia enterocolitica

Answer: (A)

Edwardsiella tarda and Salmonella share a similar biochemical profile that labs often use to identify enteric bacteria. Both are non-lactose fermenters and, importantly, both produce hydrogen sulfide, which causes blackening on certain media like triple sugar iron agar. That overlap means an isolate from stool could be misidentified as Salmonella if the testing stops after these first steps, so additional tests are typically needed to distinguish the two.

Other organisms listed have distinguishing traits that usually separate them from Edwardsiella tarda. Enterohemorrhagic E. coli generally ferments lactose and has a different toxin/social profile; Vibrio cholerae is oxidase positive and Requires different growth conditions (and is typically curved) for clear identification; Yersinia enterocolitica has its own temperature-dependent growth and motility patterns that help differentiate it from Salmonella. The closest biochemical match, and thus the most likely source of confusion in routine stool workups, is Salmonella.