An organism isolated from a stool culture displays certain reactions, including being motile, LDC positive, and indole-positive. What organism is it likely to be?

The organism likely to be isolated from a stool culture that shows motility, LDC positivity (lysine decarboxylase positive), and indole positivity is Edwardsiella tarda. This bacterium is part of the Enterobacteriaceae family and is known for these specific biochemical reactions.

Motility indicates that the organism can move through its environment, which is a characteristic of several bacteria, including E. tarda. Being LDC positive means it can decarboxylate lysine, producing ammonia and raising the pH, which is another feature of E. tarda. Additionally, the indole test being positive indicates that the organism can produce indole from the amino acid tryptophan, a characteristic that helps differentiate E. tarda from other similar organisms.

While other choices may exhibit one or more of these traits, the combination of being motile, LDC positive, and indole positive uniquely identifies Edwardsiella tarda in this context.