TCBS agar | Vibrio Selective Agar
☰ Content :
Ⅰ. Overview
Thiosulfate-Citrate-Bile Salts-Sucrose Agar, TCBS Agar, is a selective and differential culture medium which is used for the isolation and cultivation of Vibrio cholerae and others Vibrio spp. from clinical specimens, waters, food specimens and other materials.
TCBS Agar was developed by Kobayashi et al , which modified Nakanishi's selective medium. .
Vibrio cholerae on TCBS agar
Ⅱ. Preparation / Composition
Suspend the components, dehydrated powder, in water (88.1 g in 1000 ml of purified/distilled water). Bring to a boil and completely dissolve the medium. DO NOT AUTOCLAVE
Cool the medium to approximately 50°C and pour into sterile Petri dishes.
TCBS agar composition |
|||
|---|---|---|---|
| Ingredients | Gram/ liter | Ingredients | Gram/ liter |
| Sucrose | 20.0g | Dipeptone | 10.0g |
| Sodium Citrate | 10.0g | Sodium Thiosulfate | 10.0g |
| Sodium Chloride | 10.0g | Yeast extract | 5.0g |
| Oxbile (Oxgall) | 5.0g | Sodium cholate | 3.0g |
| Ferric citrate | 1.0g | Bromothymol Blue | 0.04g |
| Thymol Blue | 0.04g | Agar | 15,0 g |
Oxgall is a natural substance containing a mixture of bile salts, and sodium cholate, a pure bile salt.
Ⅲ. Principle
The high concentrations of thiosulfate and citrate and the high alkalinity of this medium largely inhibit the growth of Enterobacteriaceae.
Ox bile and sodium cholate inhibit Gram-positive bacteria.
Sodium thiosulfate also serves as a source of sulfur and its presence, in combination with ferric citrate, makes it easy to detect the production of hydrogen sulfide.
Sucrose (sucrose) is included as a fermentable carbohydrate, any coliform bacteria that may grow cannot metabolize sucrose. Only a few sucrose-positive strains of Proteus can grow to form yellow vibride-like colonies.
The mixed thymol blue-bromothymol blue indicator turns yellow when acid is formed, even in this strongly alkaline medium.
The alkaline pH of the medium improves the recovery of V.cholerae.
Ⅳ. Results
| Organisms | Growth |
|---|---|
| V. cholerae | Large yellow colonies. |
| V. parahaemolyticus | Colonies with blue to green centers. |
| V. alginolyticus | Large yellow colonies. |
| Proteus/Enterococci | Partial inhibit. When growing, colonies are small and yellow to translucent. |
| Pseudomonas/Aeromonas | Partial inhibit. If the growth colonies are blue. |
Vibrio parahaemolyticus on TCBS agar