Violet Red Bile Agar
Also known as：VRBA · V.R.B.A. · Crystal Violet Neutral Red Bile Agar · Violet Red Bile Lactose Agar · VRBL Agar
For the enumeration of coliform organisms in food, dairy products, and water.
- Category
- Dehydrated Culture Media
- Dissolve per litre
- 41.53 g
- Pack sizes
- 500 g · 5 kg · 25 kg
- Certifications
- Halal
- Standard methods
- ISO 4832
Data updated：2026-11-06
Brand cross-reference：BD Difco Violet Red Bile Agar · Oxoid Violet Red Bile Agar (VRBA) · Merck VRB Agar（ISO 4832） Brand cross-reference
Overview
Violet Red Bile Agar (VRBA) is the standard selective medium for coliform counts in food and dairy products. Bile salts and crystal violet suppress Gram-positive organisms; lactose-fermenting coliforms produce acid, turning neutral red to give purple-red colonies with a bile precipitate halo. Used by pour plate for coliform counts, it is a staple hygiene-indicator medium in dairy, beverage and food plants.
Principle
Violet Red Bile Agar is a selective and differential medium for the enumeration of coliforms by the pour-plate technique.¹ Enzymatic digest of animal tissues and yeast extract supply nitrogen, amino acids, vitamins, and growth factors, and sodium chloride maintains the osmotic equilibrium. Bile salts and crystal violet inhibit Gram-positive bacteria. Lactose is the fermentable carbohydrate, and neutral red serves as the pH indicator. Coliforms ferment lactose and produce acid, forming purplish-red colonies at least 0.5 mm in diameter, often surrounded by a reddish zone of precipitated bile. The overlay restricts spreading and creates semi-anaerobic conditions that further suppress non-coliform flora. Characteristic colonies are counted and, where required, confirmed in a lactose fermentation broth.²
How selective media fit into the testing workflow
Pathogen testing normally runs in three stages: a pre-enrichment medium such as Buffered Peptone Water repairs injured cells and raises numbers, a selective enrichment then suppresses competing flora, and finally a selective differential agar isolates the target colonies. Selective agents are typically bile salts, dyes, or antibiotics; differential agents make target colonies develop a characteristic colour or morphology. Choose the combination specified by the method you follow.
Directions
Suspend 41.53 g of powder in 1 L of purified water. Heat with continuous stirring and bring to the boil for 1 minute. DO NOT AUTOCLAVE. Cool to 45-50°C and use for the pour-plate technique with an overlay of the same medium. Test the finished medium for performance using stable, standard control cultures.
Cultural response
| Test organism | ATCC | Growth |
|---|---|---|
| Escherichia coli | 25922 | good-luxuriant |
| Klebsiella aerogenes | 13048 | good-luxuriant |
| Salmonella enterica ser. Typhimurium | 14028 | good |
| Staphylococcus aureus | 25923 | inhibited |
| Enterococcus faecalis | 29212 | inhibited |
Product highlights
- Halal certified, suitable for the Malaysian, Indonesian, and Middle Eastern markets
- Manufactured to the standard formulation, 41.53 g per litre
- Performance verified against standard control strains before release (Escherichia coli, Klebsiella aerogenes, Salmonella enterica ser. Typhimurium, Staphylococcus aureus, Enterococcus faecalis)
- Available in 500 g / 5 kg / 25 kg, from laboratory to industrial scale
- COA, specification sheet, and technical data sheet available; samples on request
- Manufactured in Taiwan with reliable supply
FDA BAM methods
This product corresponds to a medium used in the chapters of the US FDA Bacteriological Analytical Manual (BAM), the reference methods for FDA regulatory testing. Follow the current online edition of each chapter.
- FDA BAM Chapter 4: Enumeration of Escherichia coli and the Coliform BacteriaBAM Chapter 4Count plateNamed in the method as：Violet red bile agar (VRBA), solid medium method
BAM specifies methods and media formulations; it does not certify brands. Add supplements as the chapter requires, and verify media against reference strains under your quality system.
Frequently asked questions
01Does this medium meet FDA BAM methods?
BAM specifies methods and formulations, not brands. This product corresponds to a medium used in: FDA BAM Chapter 4: Enumeration of Escherichia coli and the Coliform Bacteria（BAM Chapter 4）: Count plate. It is manufactured to the standard formulation and ships with a COA per batch; add supplements as the chapter requires and follow the current online edition.
02Can selective media be autoclaved?
Not always. Some media containing dyes or selective inhibitors lose their selectivity if overheated and should only be heated until fully dissolved, without autoclaving. Follow the preparation instructions for this product, and contact us if you are unsure.
03How much powder per litre?
Use 41.53 g per litre of deionised water; preparation and sterilisation conditions are given on the specification sheet.
04Which organisms is it suitable for?
Coliforms, Gram-negative, E. coli, Escherichia coli, Klebsiella aerogenes, Salmonella enterica ser. Typhimurium, Staphylococcus aureus, Enterococcus faecalis. See the cultural response table and the specification sheet.
05What are the equivalent brand products and standard methods?
Cross-reference: BD Difco Violet Red Bile Agar, Oxoid Violet Red Bile Agar (VRBA), Merck VRB Agar. Standard methods: ISO 4832. Formulations may differ slightly between makers; refer to the specification sheet.
06How is this product prepared?
Suspend 41.53 g of powder in 1 L of purified water. Heat with continuous stirring and bring to the boil for 1 minute. DO NOT AUTOCLAVE. Cool to 45-50°C and use for the pour-plate technique with an overlay of the same medium. Test the finished medium for performance using stable, standard control cultures.
07How do I request a bulk quotation, and can you provide a COA?
Yes. This product is available in 500 g, 5 kg, 25 kg. Tell us your application and volume when requesting a quotation; we reply within one working day and can supply the COA, specification sheet, and technical data sheet.
Used in these applications
Further reading
References
- 1. ISO 4832, Microbiology of the food chain — Horizontal method for the enumeration of coliforms — Colony-count technique, International Organization for Standardization, Geneva.
- 2. American Public Health Association, Standard Methods for the Examination of Dairy Products, current edition, APHA Press, Washington, D.C.