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Violet Red Bile Agar, VRBA
Used for detection and enumeration of coliforms in food, animal feed and environmental samples.
Catalog Number: AS-1377
Violet Red Bile Agar (VRBA) is a selective and differential culture medium which is used to count and identify coliform bacteria. Bile salts and crystal violet are added to the medium to selectively inhibit the growth of Gram-positive organisms. Because lactose is the only source of carbohydrates, lactose fermenters (coliforms) can be distinguished from non-lactose fermenters.
Peptone and yeast extract provide essential nutrients for microbial growth. Neutral red serves as a pH indicator. Coliforms ferment lactose to produce acid, which changes the color and results in the production of red colonies. Bile salts precipitate due to acidification, which is one of the factors that gives coliform colonies their distinctive characterization.
Although VRBA is useful for identifying coliforms, additional biochemical testing is necessary for a definite identification.
Storage
Keep the container at 15-30 °C and prepared medium at 2-8 °C.
| Composition | gr/L |
| Peptone | 7 |
| Yeast Extract | 3 |
| Lactose | 10 |
| Bile Salts | 1.5 |
| Sodium Chloride | 5 |
| Neutral Red | 0.03 |
| Crystal Violet | 0.002 |
| Agar | 13 |
| Final pH at 25°C | 7.4 ± 0.2 |
| Dehydrated Appearance | Beige to reddish-beige, free-flowing, homogeneous. |
| Prepared Appearance | Reddish-purple, Slightly opalescent, no significant precipitate. |
| Reaction of 3.95% Solution at 25°C | pH 7.4 ± 0.2 |
| Incubate at 32 ± 1 °C for 24 ± 2 hours. | ||
| Organism (ATCC) | Recovery | Colony color |
| Escherichia coli (25922) | Good | Deep red with red precipitate around colonies |
| Enterobacter aerogenes (13048) | Good | Red, may have slight red precipitate around colonies |
| Shigella flexneri (29903) | Good | Colorless with no precipitate |
| Staphylococcus aureus (25923) | Marked to complete inhibition | – |
| Bacillus cereus (11778) | None | – |
