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Principle
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MacConkey agar is a modification of the original bile salt-neutral red-lactose agar recommended by MacConkey (1905) 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.
- Media consists of pancreatic digestion of gelatin, lactose monohydrate, sodium taurocholate, sodium chloride, neutral red, and agar. The pancreatic digest of gelatin provides essential nutrients, vitamins, and nitrogenous factors, and growth factors required for the growth of microorganisms.
- Lactose monohydrate is a carbon and energy source for gram-negative lactose-fermenting Escherichia coli and other enteric bacteria. The sodium taurocholate provides selectivity to media and inhibits the growth of most species of gram-positive organisms.
- Sodium chloride maintains the osmotic balance in the medium. Whereas the neutral red is a pH indicator, due to lactose fermentation, acid is produced and the absorption of the neutral red and subsequent color change of the dye takes place below pH 6.8. Lactose fermenting strains were observed as red or pink colored.
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