What is the most likely identification for a pediatric patient with bloody diarrhea and a clear colony on MacConkey agar with sorbitol?

The identification of a pediatric patient with bloody diarrhea and clear colonies on MacConkey agar supplemented with sorbitol points toward the presence of E. coli O157:H7. This strain is a pathogenic variant of E. coli that specifically produces Shiga toxin and is associated with hemolytic uremic syndrome.

On MacConkey agar, most strains of E. coli typically ferment lactose and produce pink colonies. However, E. coli O157:H7 is a non-lactose fermenter, which results in clear colonies, particularly when using MacConkey agar that contains sorbitol instead of lactose. This characteristic is a key differentiator since other pathogenic bacteria, like Yersinia spp., Salmonella spp., and Shigella spp., would not typically present as clear colonies under these conditions, as they have different fermentation profiles or growth requirements.

The combination of symptoms (bloody diarrhea) and the specific culture characteristics on MacConkey agar with sorbitol lead to the conclusion that E. coli O157:H7 is the most likely identification in this case.