BRILLANT GREEN BILE AGAR

Specifications

Ingredients : gms/lit.
Peptone 8.25
Lactose 1.90
Sodium sulphite 0.205
Ferric chloride 0.0295
Monopotassium phosphate 0.0153
Erioglaucine 0.0649
Basic fuchsin 0.0776
Oxgall 0.00295
Brilliant green 0.0000295
Agar 10.15
Final pH (at 25°C) : 6.9 + 0.2

Directions :
Suspend 20.7 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 45-50°C. Mix well and pour into sterile Petri plates. For plating 10 ml quantities of water samples, prepare the medium in double strength.

Principle :
Brilliant Green Bile Agar contains peptone as a source of carbon, nitrogen, vitamins and minerals. Lactose is a fermentable carbohydrate. Oxgall (bile) and brilliant green inhibit gram-positive bacteria and most gram-negative bacteria except coliforms. Erioglaucine and basic fuchsin together form the indicator system of the medium. Monopotassium phosphate is a buffering agent. Agar is a solidifying agent. Differentiation of the coliforms is based on fermentation of lactose. When the pH is neutral, colour of the medium is blue while acid production from lactose turns the medium pink and colonies appear pink to deep
red depending on the pH change. Colonies of coliform bacteria are deep red surrounded by a pink halo against blue background of the medium. Bacteria that do not ferment lactose form colorless to faint pink colonies. Coliform bacteria typically ferment lactose, producing deep red colonies, while Salmonella spp., which do not ferment lactose, produce colorless to faint pink colonies.