Violet Red Bile Agar

Violet Red Bile Agar is used for the enumeration of coliforms in food and dairy products in a laboratory setting. Violet Red Bile Agar is not intended for use in the diagnosis of disease or other conditions in humans and conforms to American Public Health Association (APHA).

The coliform group of bacteria includes aerobic and facultative anaerobic, Gram-negative, non-spore forming bacilli. Coliforms ferment lactose and form acid and gas at 35°C within 48 hours. Members of Enterobacteriaceae comprise the majority of the group, but other lactose fermenting organisms may also be included.

Procedures to detect, enumerate, and presumptively identify coliforms are used in testing foods and dairy products. One method for performing the presumptive test for coliforms uses Violet Red Bile Agar, (VRBA). If typical coliform colonies appear, they are tested further to confirm their identification as coliforms. Coliform colonies lower the pH of the medium, subsequently causing their colonies to look red (Neutral Red Dye) and to precipitate the bile salts.


Formula Liter
Yeast Extract 3 g
Enzymatic Digest of Gelatin 7 g
Bile Salts Mixture 1.5 g
Lactose 10 g
Sodium Chloride 5 g
Neutral Red 0.03 g
Crystal Violet 0.002 g
Agar 15 g

Final pH: 7.4 ± 0.2 at 25°C
Formula may be adjusted and/or supplemented as required to meet performance specifications.


  1. Suspend 41.5 g of the medium in one liter of purified water.
  2. Heat with frequent agitation and boil for two minutes. DO NOT AUTOCLAVE.
  3. Cool the medium to 45 – 46°C and dispense 15 – 20 mL into 100 mm Petri dishes containing inoculum.
  4. After solidification of the inoculated medium, evenly add a cover layer of 4 mL of the cooled (45 – 46°C) agar medium.

Order Details

Product # Product Description
7165A Violet Red Bile Agar, 500 g
7165T Violet Red Bile Agar, 5 kg