Edwardsiella tarda in stool can be biochemically mistaked for which organism?

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

Answer: (A)

The main idea here is that some enteric bacteria have very similar biochemical profiles, so they can look the same to standard lab tests used on stool samples. Edwardsiella tarda and Salmonella share several key characteristics—both are Gram-negative, non-spore-forming rods that are oxidase negative and non-lactose fermenters, and both can produce hydrogen sulfide on certain culture media. Because of these overlapping traits, an initial biochemical workup can lead to a misidentification, with Edwardsiella tarda being labeled as Salmonella until more specific, distinguishing tests are done or molecular methods confirm the genus. It helps to remember that Edwardsiella tarda is mainly associated with aquatic sources, while Salmonella is a more common human pathogen, which is why labs often pursue further testing to avoid this particular mix-up.