Which organism, found in normal fecal flora, may be mistaken biochemically for the genus Yersinia?

• A. Klebsiella spp.
• B. Proteus spp.
• C. E. coli
• D. Enterobacter spp.

Answer: (B)

Proteus species are part of the normal fecal flora and can exhibit biochemical characteristics that may lead to confusion with Yersinia species. Both genera can be indole-positive, urease-positive, and exhibit similar reactions in certain biochemical tests. For instance, both Yersinia enterocolitica and some species of Proteus can ferment sugars similarly, which may obscure their differentiation in a laboratory setting.

The biochemical characteristics of Proteus, especially its motility and sulfur production, can lead to challenges when identifying these organisms, particularly if the initial tests do not provide definitive results. In contrast, the other organisms listed, such as Klebsiella, E. coli, and Enterobacter, have more distinct biochemical profiles that make them less likely to be confused with Yersinia. This makes Proteus spp. a prime candidate for confusion in biochemical testing related to Yersinia identification.