Brilliant Green Agar (BGA) is used for the selective isolation of Salmonella spp, other than S. typhi, in foods and clinical specimens, via Lactose/Sucrose fermentation. The Peptone mixture provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly the B-group. Sucrose and Lactose are fermentable carbohydrates providing carbon and energy. Phenol red is the pH indicator, turning the medium a yellow color with the formation of acid as a result of Lactose/Sucrose fermentation. Brilliant green inhibits Gram-positive bacteria and most Gram-negative bacilli, other than Salmonella spp. Lactose/Sucrose fermenters are usually inhibited. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Bacteriological agar is the solidifying agent. The medium, which has a coffee color at the beginning, changes to red during incubation at 35-37 ºC. A probable presence of Salmonellae is indicated by small, transparent, either colorless or pink or opaque-white colonies, often surrounded by a pink or red zone. Some of the uninhibited Gram-negative, Lactose/Sucrose fermenting organisms present opaque green-yellow colonies, surrounded by a yellow halo. Other lactose negative microorganisms, such as Proteus spp., form colonies of a pale pink or red color, transparent and surrounded by a brilliant red halo.
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