What type of agar is selective for Vibrio species, including those in the Enterobacteriaceae family?

• A. MacConkey agar
• B. Thiosulfate-citrate-bile salts-sucrose (TCBS) agar
• C. Blood agar
• D. Nutrient agar

Answer: (B)

Thiosulfate-citrate-bile salts-sucrose (TCBS) agar is specifically designed to isolate and differentiate Vibrio species, which are a part of the broader category of Enterobacteriaceae. This agar contains high concentrations of bile salts and citrate, which inhibit the growth of most Gram-positive bacteria and many Gram-negative bacteria, thus creating a selective environment for Vibrio species.

The addition of sucrose in TCBS agar allows for the fermentation of sucrose by certain Vibrio species, leading to color changes that help differentiate between them. For instance, Vibrio cholerae ferments sucrose and produces yellow colonies, while non-sucrose-fermenting species appear green.

In contrast, other types of agar, such as MacConkey agar, are selective for Gram-negative bacteria in general, particularly Enterobacteriaceae, but are not specific for Vibrio. Blood agar is a general-purpose medium that supports the growth of a wide variety of organisms, including both Gram-positive and Gram-negative bacteria, making it less selective for Vibrio. Nutrient agar is also a non-selective medium that supports the growth of many types of bacteria without targeting any specific group.

Therefore, TCBS agar is the most appropriate choice