Which rapid test differentiates Plesiomonas shigelloides from Shigella species?

The rapid test that effectively differentiates Plesiomonas shigelloides from Shigella species is the oxidase test. Plesiomonas shigelloides is a facultatively anaerobic, oxidase-positive bacterium, whereas Shigella species are oxidase-negative. This fundamental biochemical characteristic allows for the clear differentiation between these two genera.

In practical terms, when performing the oxidase test on a culture, the addition of an oxidase reagent will result in a color change (typically purple) if the organism possesses cytochrome c oxidase, indicating its positive result. Conversely, Shigella species will not exhibit this color change, confirming their oxidase-negative status.

This differentiation is crucial in clinical microbiology for accurate identification and appropriate treatment since Plesiomonas shigelloides can be associated with diarrhea and may require different antibiotic considerations compared to Shigella species.