Mineral Modified Glutamate Medium Base (Double Strength) (Twin pack)

Principle And Interpretation

MacConkey Broth was originally used for enumeration of coliform bacteria in water. However Folpmers (1) described a glutamic acid based chemically defined medium for the same. This glutamate-containing medium was later modified by Gray (2), by the addition of lactose, which gave less false positive results when compared to MacConkey Broth. To improve gas production in the medium, it was supplemented with ammonium chloride (3). Mineral Modified Glutamate Medium is used for the enumeration of coliform bacteria in water. This medium gave better results than MacConkey Broth (with less false positives) while testing water samples, both chlorinated and unchlorinated (4). Mineral Modified Glutamate Medium is superior to other media, in testing for coliforms and Escherichia coli because it initiates faster growth. This medium is recommended by APHA (7) and is also used to enrich coliform organisms present in cheese and meat (5).

This medium contains a variety of nutrients including salts, amino acids and vitamins. Lactose is the fermentable carbohydrate and bromo cresol purple is the pH indicator. Because of the nutrients, this medium is superior for enumerating coliforms in water and wastewater as it satisfies most of the nutritional requirements of coliforms.

If the test water sample is supposedly of good quality, inoculate 50 ml water sample in 50 ml of medium. Also inoculate 5 tubes of 10 ml Mineral Modified Glutamate Medium Base (M643), each with 10 ml water sample. If water sample is more polluted, inoculate 5 tubes of 5 ml of single strength medium each with 1 ml of a 1: 10 dilution of the sample. Incubate the tubes at 35-37°C for 18-24 hours. Tubes showing yellow colouration, due to acid production and gas formation, (bubbles trapped in Durhams tubes) are presumptively positive. These should be further confirmed by inoculating into Brilliant Green Bile Broth 2% (M121) and by performing biochemical tests.

MPN per 100 ml of water sample can be calculated by referring to MPN Chart (6).