What characteristic feature is noted for Vibrio parahaemolyticus on TCBS agar?

Vibrio parahaemolyticus is a marine bacterium that is known to cause gastrointestinal illnesses and is commonly isolated from seafood. When cultured on Thiosulfate Citrate Bile Salts Sucrose (TCBS) agar, this organism exhibits a distinct characteristic: it produces blue/green colonies.

The reason for this coloration lies in the composition of TCBS agar. This selective medium is designed to isolate Vibrio species from clinical and environmental samples. It contains sucrose as a fermentable carbohydrate, thiosulfate to inhibit gram-positive bacteria, and dyes that indicate sucrose fermentation. Vibrio parahaemolyticus does not ferment sucrose, which aligns with its unique biochemical profile. Instead, it produces a blue/green hue on the medium due to its ability to utilize other sources of carbon, leading to an alkaline reaction that further contributes to the coloration.

This recognition of blue/green colonies is crucial for microbiologists, as it helps in the rapid identification of Vibrio parahaemolyticus from clinical specimens, particularly when correlating with clinical symptoms of foodborne disease associated with seafood consumption.