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Principle
- Violet red bile lactose agar is recommended by APHA (1978) and ISO (1991). Violet red bile lactose agar contains yeast extract, a pancreatic digest of gelatin, bile salts, sodium chloride, lactose, neutral red, crystal violet, and agar.
- The pancreatic digest of gelatin serves as a source of carbon, nitrogen, vitamins, and minerals. Yeast Extract supplies additional nitrogen, carbon, and vitamins which stimulate bacterial growth. Lactose is a source of carbohydrates.
- Bile salts and crystal violet perform inhibitory action and inhibit gram-positive bacteria. The fermentation of lactose to acid is indicated by the pH indicator neutral red, which changes its color to red, and by the precipitation of bile acids. Organisms that rapidly attack lactose produce red-purple colonies surrounded by
- purple haloes. While the Non-fermenters or late lactose-fermenters produce pale colonies with greenish zones. Agar is a solidifying agent.
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Use: Recommended for selective isolation, detection, and enumeration of coli-aerogenes bacteria in food and water, milk other dairy food products and clinical samples.
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