VetBact logo


Swedish University of Agricultural Sciences

Veterinary bacteriology: information about important bacteria
Veterinary bacteriology

Show all growth media

Violet red bile agar (VRB agar)

Violet red bile agar (VRB agar) [under revision]

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:

  • peptone (contains amino acids and peptides)
  • yeast extract (contains peptides, sugars, minerals and B vitamins)
  • NaCl (contributes to the osmotic balance)
  • bile salts (inhibit gram positive bakteria)
  • lactose (carbon source)
  • neutral red (pH-indicator)
  • crystal violet (inhibit gram positive bakteria)
  • agar (gelifying agent)
  • water

The final pH of the medium should be 7.4.

Other comments:

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.

Updated: 2023-05-31.

Recently Updated

Recent blog posts

Most recent comment

Swedish University of Agricultural Sciences