Description
A number of modifications have been made to the original chemically defined medium based on glutamic acid, postulated by Folpmers1 for the estimation of coliforms in water. Results of a trial conducted by the Public Health Laboratory Service in 1958, indicated that glutamic acid media containing glucose produced an unacceptably high number of false positive results in 48 hours2.
Subsequently, Gray modified a glutamate medium containing lactose and in 1964 reported an improved Formate Lactose Glutamate Medium3. The Public Health Laboratory Service (PHLS) embarked on a large trial incorporating three formulations for glutamate medium, Teepol Broth4 and MacConkey Broth5 which demonstrated that Gray’s improved Formate Lactose Glutamate Medium was superior to the other formulations trialed. However, they also suggested that modification of the mineral content in Gray’s formulation could improve results, and a group investigation was initiated resulting in the present formulation, which the PHLS trialed and found to be superior to MacConkey Broth for the detection of E. coli. These results, however, indicated that for chlorinated water using glutamate media, an incubation period of more than 18 hours was required for optimum performance. Further trials have shown that Lauryl Tryptose Broth provides an earlier result (18-24 hours) but Minerals Modified Glutamate Base is superior in the detection of small numbers of E. coli in other water samples7. Papadakis found that Minerals Modified Glutamate Base gave superior results to MacConkey Broth for the investigation of sea water but that it was necessary to dilute sea water 1 volume to MMGB 10 volumes, to dilute the high level of salt8.
Note: Minerals Modified Glutamate Base was developed for use with water samplesa and adaptation of methods for use with milk or food samples may not give comparable results because nutrients in these products may influence the action of the medium
