The Violet Red Bile Glucose Agar, is a selective medium used for detecting and enumerating Enterobacteriaceae in food, water, and other materials. This agar is consistent with the standards of the United States Pharmacopoeia (USP), European Pharmacopoeia (EP), Japanese Pharmacopoeia (JP), and ISO 21528.
Composition and Principle
The typical formulation of Violet Red Bile Glucose Agar includes Enzymatic Digest of Animal Tissues, Yeast Extract, Glucose, Sodium Chloride, Bile Salts, Neutral Red, Crystal Violet, and Agar. The medium’s pH is set at 7.4 ± 0.2 at 25°C. The Enzymatic Digest of Animal Tissues and Yeast Extract provide essential nutrients, while Glucose serves as the fermentable carbohydrate. Sodium Chloride maintains the osmotic balance. Bile Salts and Crystal Violet act as selective agents against Gram-positive cocci, and Neutral Red is the pH indicator.
Preparation
The preparation involves suspending 40.5 g of the powder in 1 liter of distilled or deionized water, heating it to boiling until fully dissolved, and then cooling it to 45-50°C. It’s important not to autoclave the medium. Once prepared, the agar is poured into Petri dishes for inoculation.
Test Procedure
The test procedure includes using a suitable diluent, such as Buffered Peptone Water, for sample preparation. The sample is then inoculated on the Violet Red Bile Glucose Agar using pour plating or spread plating methods. The medium is incubated aerobically at 30-35°C for 18-24 hours or at 37°C for 24 ± 2 hours. For environmental hygiene monitoring, a swab and a sampling template can be used to sample a defined area of the test surface.
Interpreting Results
Results are interpreted by counting characteristic pink to red colonies (with or without a precipitation halo). Confirmatory tests, such as oxidase reaction and glucose fermentation, are conducted on non-selective agar media to confirm the presence of Enterobacteriaceae.
Appearance
The dehydrated medium appears as a free-flowing homogeneous beige to reddish-beige powder, while the prepared medium is slightly opalescent reddish-purple.
Storage
The dehydrated medium should be stored at 10-30°C in a dry environment and in its original container. Prepared plates and bottles should be stored at 10-25°C away from light.
Quality Control
Quality control testing should be carried out following specific requirements for the method used. The medium’s performance is verified using control strains such as Escherichia coli (WDCM 00012 or 00013) and Salmonella Typhimurium (WDCM 00031).
Warnings and Precautions
Though not classified as hazardous under current legislation, it is recommended to consult the safety data sheet for proper use. The product is intended for professional use only and should be used by adequately trained operators.
Disposal of Waste
Waste disposal must be conducted according to national and local regulations.
Violet Red Bile Glucose Agar is a vital tool in the microbiological examination of food, water, and other materials, offering a reliable method for detecting and enumerating Enterobacteriaceae. Its formulation, ease of use, and adherence to international standards make it an indispensable medium in various laboratory settings.
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