Bromocresol purple lactose agar | BCP Agar

Ⅰ. Overview

Bromocresol purple lactose agar, BCP Agar, is a lactose-based, differential, non-selective medium used for the detection and isolation of Enterobacteriaceae. It (also) makes it possible to differentiate the species fermenting lactose from those which do not ferment it.

Lactose acts as a carbohydrate source, while bromcresol violet is a pH indicator. The latter gives a purple color to the medium, and turns yellow if the lactose in the medium is used by the bacteria.

This medium is commonly used during the bacteriological examination of urine, stool, food, dairy products and water samples.

Ⅱ. Composition of Bromocresol purple lactose agar

Suspend the components, dehydrated powder, in water (28 grams in 1000 ml of purified/distilled water). The medium is boiled for a few seconds until the ingredients are completely dissolved. Mix well and finally sterilize by autoclaving at 121°C for 15 minutes.

Cool to 45-50°C and dispense aseptically into sterile Petri dishe. Date the medium and assign it a lot number.

Ⅲ. Interpretation

All coliforms, Escherichia, Enterobacter, Citrobacter and Klebsiella, ferment lactose with production of acid and gas.

When lactose is fermented, it produces an acid that changes color from mid blue-purple (alkaline) to yellow (acid). The blue colonies are lactose-negative and the yellow ones are lactose-positive.