Which agar is the standard choice for isolating Yersinia from stool specimens?

The standard choice for isolating Yersinia from stool specimens is MacConkey agar. This medium is selective for Gram-negative bacteria and inhibits the growth of Gram-positive organisms, making it particularly useful for isolating enteric pathogens like Yersinia.

Yersinia enterocolitica, the species commonly associated with gastrointestinal infections, can ferment lactose, but its colonies typically appear colorless or pale on MacConkey agar, allowing for easy differentiation from other lactose fermenters, which appear pink. This helps in effectively isolating Yersinia while also identifying potential co-inhabiting flora in stool samples.

While other media like Salmonella-Shigella agar, Hektoen enteric agar, and CNA agar can also be used for isolating various enteric pathogens, they may not provide the same level of specificity or the ideal conditions for Yersinia growth and isolation compared to MacConkey agar. Each of these alternatives serves different purposes; for instance, Salmonella-Shigella agar is designed specifically for isolating Salmonella and Shigella spp., and CNA agar is selective for Gram-positive bacteria.