Thiosulfate–citrate–bile salts–sucrose agar

TCBS agar plate of Vibrio Cholerae and vibrio parahaemolyticus

Thiosulfate–citrate–bile salts–sucrose agar (TCBS agar) is a selective medium used in microbiology for the isolation of Salmonella and Shigella species. It is a specialized agar medium that contains specific components to inhibit the growth of unwanted bacteria while promoting the growth of the target organisms.

Composition

The composition of TCBS agar includes:

• Sodium thiosulfate
• Sodium citrate
• Bile salts
• Sucrose
• Agar

Principle

TCBS agar works by providing a selective environment that favors the growth of Salmonella and Shigella species. The sodium thiosulfate and citrate inhibit the growth of Gram-positive bacteria, while the bile salts suppress the growth of most Gram-negative bacteria. The sucrose in the medium serves as a fermentable carbohydrate for the target organisms.

Application

TCBS agar is commonly used in clinical laboratories for the isolation and identification of Salmonella and Shigella species from clinical samples, such as stool specimens. The distinctive yellow color of colonies formed by these organisms on TCBS agar aids in their differentiation from other bacteria.

Interpretation

On TCBS agar, Salmonella species typically produce yellow colonies with or without black centers, while Shigella species form green colonies. The characteristic appearance of colonies on TCBS agar helps microbiologists identify and differentiate these pathogens.

See also

• Salmonella
• Shigella
• Agar plate

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