Brilliant Green Bile Agar can be used to assess the degree of contamination of water samples, diverse foods and other products. It uses basic fuchsin to differentiate between lactose-fermenting and lactose non-fermenting bacteria. Acid production by lactose fermenting organisms, such as Escherichia coli, produce characteristic red colonies with a pink surrounding area. Lactose non-fermenters form colorless and transparent colonies. The gelatin peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Lactose is the fermentable carbohydrate providing carbon and energy. Ox bile and brilliant green inhibit gram-positive bacteria and most gram-negative bacteria except coliforms. Erioglaucine and basic fuchsin together indicate pH of the medium. Monopotassium phosphate acts as a buffer system. Bacteriological agar is the solidifying agent. For the enumeration of coliform bacteria employ sample dilutions, which yield between 10-50 colonies per plate using the pour plate method. Incubate at 35Â±2 °C for 18-24 hours. The coliform colonies have an intensely red center zone surrounded by a pink halo which is sharply outlined against the uniformly blue background of the medium. Salmonella spp, which do not ferment lactose, produce colorless to pale pink colonies. The medium is sensitive to light, which reduces its effectiveness and changes its color from strong blue to purple or pink. The medium should be prepared immediately before use and, if necessary, stored in the dark for the least time possible.
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