Violet red bile agar (VRB agar)
The figure shows a VRG agar plate on which coliform bacteria have been cultivated. - Click on the image to enlarge it.
Image: Ingrid Hansson (SLU), Lise-Lotte Fernström (SLU) & Karl-Erik Johansson (SLU).
Violet red bile agar (VRB agar) is a selective medium, which is used for enumeration of coliform bacteria in water, milk and other dairy produts.
The medium contains:
The final pH of the medium should be 7.4.
VRB agar is often used in combination with TSA (Tryptone Soya Agar) for the detection and enumeration of thermotolerant coliform bacteria (including E. coli). A thin layer of TSA (containing the sample with bacteria) is then molded in the bottom of the plate, which is then incubated for 1-2 h. at ambient temperature. Another layer consisting of VRG-agar is then molded on top on the TSA and the plate is incubated further.