Brilliant Green Bile Agar

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 the 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 35 ± 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.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 20.6 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 45-50 °C, mix well and dispense into plates.

Instructions for use

Inoculate and incubate at a temperature of 35 ± 2 °C for 18-24 hours.

• Methods for the Examination of Water and Wastewater, 10th Ed APHA, Inc. New York, 1958.
• Recommended Methods for the Microbiological Examination of Foods, APHA, Inc. New York, 1958.