TCBS Agar- Composition, Principle, Preparation, Results, Uses


Thiosulfate-citrate-bile salts-sucrose (TCBS) Agar is a selective and differential medium for the isolation and identification of Vibrio species, especially Vibrio cholera, the causative agent of cholera. Cholera is an acute diarrheal disease that can be fatal if left untreated. Vibrio cholerae is a gram-negative, comma-shaped, facultative anaerobic bacterium that produces a potent enterotoxin that affects the intestinal mucosa.

TCBS Agar was developed by Kobayashi et al. in 1963 as an improvement over the previous media used for Vibrio isolation, such as alkaline peptone water and taurocholate-tellurite-gelatin agar. TCBS Agar has several advantages over these media, such as:

  • It has a high pH (8.6) that inhibits the growth of most other bacteria, except for some alkalophilic species.
  • It contains bile salts and sodium citrate that further suppress the growth of gram-positive bacteria and coliforms.
  • It contains sucrose as a fermentable carbohydrate that allows the differentiation of Vibrio species based on their ability to ferment it. Vibrio cholera and Vibrio mimicus produce yellow colonies due to acid production from sucrose fermentation, while other Vibrio species produce blue-green colonies due to alkaline by-products.
  • It contains sodium thiosulfate and ferric citrate that enable the detection of hydrogen sulfide production by some Vibrio species, such as Vibrio vulnificus and Vibrio parahaemolyticus. These species produce black-centered colonies due to the formation of ferrous sulfide.
  • It contains bromthymol blue and thymol blue as pH indicators that change color according to the acid-base reaction of the medium.

TCBS Agar is widely used in clinical microbiology, food microbiology, environmental microbiology, and veterinary microbiology for the isolation and identification of Vibrio species from various samples, such as stool, water, seafood, fish, and animal tissues. TCBS Agar is also useful for monitoring outbreaks of cholera and other vibriosis infections in humans and animals. However, TCBS Agar has some limitations and considerations for its use, which will be discussed in the later sections of this article.