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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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