Violet Red Bile Agar With Glucose and Lactose (VRBLG) USP

Gelatin pancreatic digest provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Lactose and glucose are the energy source carbohydrates. Bile salts and crystal violet inhibit Gram-positive bacteria. Neutral red is a pH indicator. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Bacteriological agar is the solidifying agent.

Preparation

Suspend 51.5 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Cool to 45 °C and use immediately. The medium can also be dispensed and sterilized in the autoclave at 118 °C for 15 minutes.

Instructions for use

For the detection of Enterobacteriaceae:

1. Prepare the sample using Lactose Broth (LC-1206), homogenize and incubate at 35 ± 2 °C for 2-5 hours, time enough to revive bacteria but not sufficient for growth.
2. After mixing with Mossel EE Broth (LC-1202) in a 1:100 mL ratio and incubating at 35 ± 2 °C for 18-24 hours, subculture onto VRBLG Agar to obtain selective isolation.
3. Incubate at 35 ± 2 °C for 18-24 hours.

For the enumeration of Enterobacteriaceae:

1. Inoculate the sample in Mossel EE Broth (dilutions 0.1, 0.01, 0.001 mL) and incubate at 35 ± 2 °C for 24-48 hours.
2. Subculture on plates of VRBLG Agar to obtain selective isolation.
3. Incubate at 35 ± 2 °C for 18-24 hours.
4. Growth of well-developed red colonies of Gram-negative bacteria constitutes a positive result.
5. Refer to the appropriate reference for further identification tests.

• European Pharmacopoeia 6.0
• Hitchins, A.D., P.A. Hartman, and E.C.D. Todd. 1992. Coliforms - Escherichia coli and its toxins, p. 325-369. In Vanderzant, C., and D.F. Splittstoesser (ed.) Compendium of methods for the microbiological examination of foods, 3rd ed. American Public Health Association, Washington, DC.