Principle
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MacConkey agar is a modification of the original bile salt-neutral red-lactose agar recommended by MacConkey (1905) and is prepared in accordance with the harmonized principles of USP/EP/IP and used for selective isolation and differentiation of Escherichia coli and other enteric bacteria in pharmaceutical testing and microbial limit testing of pharmaceutical products and raw material used in pharmaceutical industries.
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Media consists of pancreatic digestion of gelatin, peptone (meat and casein), lactose monohydrate, sodium chloride, bile salts, neutral red, crystal violet, and agar.
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The pancreatic digest of gelatin and peptone provides essential nutrients, vitamins, nitrogenous factors, and growth factors required for the growth of microorganisms.
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Lactose monohydrate is a carbon and energy source for gram-negative lactose-fermenting Escherichia coli and other enteric bacteria.
- The bile salts and crystal violet provide selectivity to media and inhibits the growth of most species of gram-positive organisms. Sodium chloride maintains the osmotic balance in the medium.
- Whereas, neutral red is a pH indicator. Due to lactose fermentation, acid is produced, and the color of neutral red changes. Lactose fermenting strains are observed as red or pink colored and may be surrounded by a zone of acid-precipitated bile salts.
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