What characteristic color indicates Vibrio cholerae on TCBS agar?

Vibrio cholerae is known to produce yellow colonies when grown on Thiosulfate Citrate Bile Salts Sucrose (TCBS) agar. This selective medium is specifically designed to isolate vibrios from other Gram-negative bacteria. The agar contains high concentrations of sodium thiosulfate and sodium chloride, allowing the growth of halophilic vibrios while inhibiting the growth of non-vibrios.

The yellow color of the colonies results from the fermentation of sucrose, which produces acid and lowers the pH of the agar, leading to a color change due to the pH indicator present in the medium. This characteristic yellow colony formation is a defining feature for identifying Vibrio cholerae, making it distinct from many other bacteria that do not ferment sucrose in the same way. Thus, the competence to identify Vibrio cholerae based on its yellow colonies on TCBS agar is essential in clinical microbiology for diagnosing cholera infection.