Brilliant Green Agar

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 °C. 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.

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

Preparation

Suspend 58.1 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. If necessary, allow to dry for approximately 2 hours with the covers partially removed.

Instructions for use

1. Use standard procedures to obtain isolated colonies.
2. When there is a suspicion that the material under study contains low concentrations of Salmonellae, it is necessary to initially inoculate the sample in Brilliant Green Tetrathionate Broth (LC-1253) or Selenite Cystine Broth (LC-1220) as a pre-enrichment step.
3. Incubate at 35 ± 2 °C for 18-24 hours.

• European Pharmacopoeia. 6th Ed. 2007.
• American Public Health Association. Standard Methods for the Examination of Water and Wastewater, 11th Edition APHA, New York, 1960.
• American Public Health Association. Recommended Methods for the Microbiological Examination of Foods, APHA, Inc. New York, 1958.