For selective isolation, detection and enumeration of coli aerogenes gram negative bacteria. Dissolve 50.63gms in 1000ml distilled water. Gently heat to boiling with gentle swirling and dissolve the medium completely. DO NOT AUTOCLAVE. Cool to 45ºC and immediately pour into sterile Petri plates. Appearance: Reddish-purple, clear to slightly opalescent -: pH (at 25ºC): 7.4 ± 0.2
VIOLET RED BILE AGAR W/GLUCOSE & LACTOSE (as per USP) is used for the selective isolation, detection and enumeration of coli aerogenes gram negative bacteria. Pancreatic digest of Gelatin and Yeast extract are a source of nitrogen, sulphur, carbon, vitamins and minerals. Bile salts and crystal violet are the inhibitors of gram-positive microorganisms. Glucose and Lactose is the fermentable carbohydrate. Neutral red change to red-purple due to the building of acid during fermentation which change the pH. Sodium chloride is for the osmotic balance. It relies on the use of the selective inhibitory components like, Crystal violet and Bile salts and the indicator system lactose, and neutral red. Other gram-negative bacteria can be suppressed by incubation at temperature over 42°C for 18 hours or anaerobic incubation. Agar is the solidifying agent. Lactose fermenting coliforms give red colonies with precipitation of bile salts. Lactose non-fermenters and late lactose fermenters produce pale colonies. Pour plate method is to be used for the enumeration of Enterobacteriaceae members. By pouring 1ml of the desired dilution onto a sterile agar Petri plate, adding 15 ml of the medium, cooled to 45 – 50°C, and rotating gently before allowing solidifying. Once solidified, pour a second layer of the medium to a depth of 5mm. Allow to solidify. Incubate at temperatures of 35 ± 2°C for 18 – 24 hours. With a sterile micropipette transfer 1ml of liquid product or the appropriate dilutions to the centre of each dish. Rotate it gently. Use another sterile pipette to inoculate each dilution into the dishes. Pour about 15ml of VRBL medium, at 44 °C to 47°C, into each Petri plate. The time elapsing between the end of the preparation of the initial suspension (or of the 10-1 dilution if the product is liquid) and the moment when the medium is poured into the dishes should not exceed 15 min. Carefully mix the inoculum with the medium and allow the mixture to solidify with the Petri plates standing on a cool horizontal surface.