thiosulfatecitratebile

Thiosulfate-citrate-bile-salt-sucrose agar, commonly abbreviated TCBS agar, is a selective differential culture medium used primarily for isolation and preliminary differentiation of Vibrio species from clinical, environmental, and food samples. It is designed to suppress most competing enteric bacteria while promoting the growth of Vibrio species.

The medium contains bile salts that inhibit many non-Vibrio organisms and an alkaline pH to favor Vibrio growth. It uses sucrose as the sole fermentable carbohydrate, with a pH indicator that changes color in response to acid production. Consequently, organisms that ferment sucrose produce yellow colonies or surrounding yellow halos due to the localized acidification of the medium, whereas non-sucrose fermenters or non-Vibrio bacteria typically grow as green to blue-green colonies. Some Vibrio species may appear green if they do not ferment sucrose strongly.

Interpretation of results is used as a presumptive screen. Yellow, rapidly fermenting Vibrio colonies, especially when accompanied by characteristic colony morphology, are suggestive of V. cholerae, while other vibrios may appear differently. However, TCBS is not a definitive identification method. Confirmation often requires additional biochemical tests, oxidase testing, serotyping, or molecular methods such as PCR.

Applications include routine surveillance and diagnostic workflows in clinical microbiology, public health, and environmental microbiology. TCBS agar is particularly valued for its ability to enrich Vibrio species from specimens with mixed flora, such as stool, seawater, seafood, and sediment. Limitations include occasional growth of non-Vibrio organisms and the possibility of atypical coloration for certain Vibrio strains, necessitating further testing for accurate speciation.