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Principle
- MacConkey agar without crystal violet and salt is a modification of MacConkey agar, composed of peptone, lactose, sodium taurocholate, neutral red, and agar.
- Peptones provide nitrogen and other nutrients necessary for the growth of microorganisms. Lactose is a carbon source and plays an important role in the selection of lactose-fermenting microbes. Sodium taurocholate is a selective agent, inhibits the growth of gram-positive organisms.
- Neutral red is a pH indicator dye. Agar is the solidifying agent. Due to the absence of salts, the medium becomes differential, which restricts the swarming of Proteus species, and in addition, it does not contain crystal violet, allowing Staphyloccocus and Enterococcus species to grow.
- When lactose is fermented, acid is produced which results in pH reduction and sodium taurocholate precipitation. Since the lactose fermenting colonies of coliform bacteria are pink in color and may be surrounded by a zone of sodium taurocholate precipitation.
- The pink or red color is due to the production of acid from lactose and the absorption of neutral red. Lactose non-fermenting strains, such as Shigella and Salmonella are colorless and transparent and typically do not alter the appearance of the medium.
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Use: Recommended for isolation and differentiation of lactose fermenting and lactose non-fermenting gram-negative enteric bacilli from pharmaceutical, clinical and non-clinical samples, dairy, food, and water samples.
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