Improved differentiation and enumeration of E. coli and other coliforms in drinking water

Thermo Scientific Limited has launched a new medium that enables the differentiation of E .coli and other coliform colonies by a simple colour change. Thermo Scientific MLGA (Membrane Lactose Glucuronide Agar) simplifies the membrane filtration method for E. coli and coliforms by reducing the number of filtration stages required from two to one and by reducing the need for further confirmation steps. This offers significant time savings and allows faster reporting of results.

The chromogenic substrate in Thermo Scientific MLGA, 5-bromo-4-chloro-3-indolyl-b-D-glucuronide (BCIG), is cleaved by the enzyme b-glucuronidase and produces a blue chromophore that builds up within the bacterial cells. In addition, the incorporation of phenol red detects lactose fermentation and results in yellow colonies when acid is produced. Since coliform colonies are lactose positive, they will appear yellow on this medium and as E. coli colonies are both lactose and beta-glucuronidase positive, they will appear green.

Not only does Thermo Scientific MLGA simplify the differentiation and enumeration of E.coli and coliforms by reducing the number of plates required but, since the chromogen is so specific, it also eliminates the need for further confirmation of green E. coli colonies. This allows E. coli results to be reported at an earlier stage.

MLGA is described in the Environment Agency's report, 'Methods for Examination of Waters and Associated Material - The Microbiology of Drinking Water 2002'. This report describes tests for coliforms and E. coli as the most important routine microbiological examinations carried out on drinking water. They provide the most sensitive means for the detection of faecal contamination, for assessing the effectiveness of water treatment and disinfection, and for monitoring water quality in distribution [1].

References
[1]. The Environment Agency - Methods for Examination of Waters and Associated
Material - The Microbiology of Drinking Water 2002.