MacConkey Agar w/o Crystal Violet & w/o NaCl is a differential medium used for the detection and isolation of enteric microorganisms. The lack of sodium chloride provides an electrolyte deficient medium preventing Proteus spp. from spreading (swarming), aiding the detection and isolation of enteric microorganisms. Also, as this medium does not contain Crystal violet, staphylococci, enterococci and Mycobacteria species are able to grow well. Gelatin peptone and peptone mixture provide nitrogen, vitamins, minerals and amino acids essential for growth. Lactose is the fermentable carbohydrate providing carbon and energy. Bile salts are the selective agents and inhibit Gram-positive organisms. Neutral red is the pH indicator. When lactose is fermented, the pH of the medium decreases, changing the color of neutral red into pink. Bacteriological agar is the solidifying agent.
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