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Violet Red Bile Glucose (VRBG) agar
The figure shows three VRBG agar plates. Bacteria have not been cultivated on the plate in image A. Two different members of the family Enterobacteriaceae have been cultivated at 37°C during 24 h on the plates B and C. A halo can be discerned around the colonies because of precipitated bile salts, which also makes the colonies look unsharp. This is particularly evident on the plate in image C.
Violet Red Bile Glucose (VRBG) agar is a selective medium, which is used for isolation and enumeration of members of the family Enterobacteriaceae in food products.
Content of the medium:
The final pH of the medium should be 7.4.
Members of the family Enterobacteriaceae produce small (1-2 mm in diameter), round and violet to pink colonies with a halo on VRBG agar. There are some other genera, which also grow on VRBG agar, e.g. Aeromonas. The identity of the colonies must, therefore, be confirmed by an independent method, e.g. the oxidase test.