MacCONKEY BROTH (as per USP/EP/JP/BP)

MacConkey Broth is a modification of MacConkey Medium. Childs and Allen demonstrated the inhibitory effect of neutral red and therefore substituted it by the less inhibitory bromocresol purple dye. BCP is more sensitive in recording pH variation in the medium. This medium is prepared in accordance with the harmonized method of USP/EP/JP/BP/IP.

MacConkey Broth is a selective culture medium for detecting and enumerating coliforms in pharmaceutical samples. This broth is a modification of the conventional MacConkey medium to improve its sensitivity and reduce the inhibitory effect against target organisms. MacConkey Broth is more widely accepted in microbiological testing and is prepared according to harmonized testing method USP, EP, JP and BP for use in regulated laboratories environments. MacConkey Broth is based on a simple principle that permits clear discrimination of lactose fermenting and non fermenting organisms. It has a pancreatic digest of gelatin which acts as a source of nitrogen and other nutrients required for growth of the bacteria. Lactose is provided as a fermentable carbohydrate for Gram negative bacteria. The medium contains bromocresol purple as a pH indicator, which is more sensitive to pH alterations than other dyes. Growth of lactose fermenting organisms is accompanied with the production of acid which lowers the pH below 6.8, causing the medium to change from purple to yellow. This color change helps in identifying coliform bacteria. However, non lactose fermenters like Salmonella and Shigella do not produce the colour change and the medium remains the same. Dehydrated ox bile, which is another essential ingredient of MacConkey Broth, also suppresses the growth of gram positive bacteria, making it selective for Gram negative organisms. The selective property of the medium is useful in distinguishing coliforms from other organisms in mixed populations. The preparation of MacConkey Broth is easy and convenient. The medium is dissolved in distilled water, heated, and then poured into test tubes with inverted durham tubes for detection of gas. The medium is sterilized by autoclaving and cooled. The prepared medium appears purple and clear to slightly opalescent. MacConkey Broth is routinely employed in quality control and microbial examination. It performs consistently when used as directed and is useful in the identification of coliforms through observation of color change and growth patterns.

for detection enumeration of coliform bacteria