A comparison of media for the detection of coliform organisms in water

Abstract

Five media—MacConkey broth, lactose broth, Teepol broth, lauryl sulphate broth and glucose glutamic acid medium—have been compared as primary media for the isolation of coliform organisms from 1691 samples of water received for examination during a period of 18 months.Of these samples 1043 (61·7%) gave an identical result in all five media. In the other 648 (38·3%) samples there were differences either in the types of coliform organism isolated or in the rapidity with which the reactions appeared in the different media. The differences in the final yields of coliform organisms andEscherichia coliin the five media are not statistically significant.There were differences in the number of false presumptive positive reactions given by the different media—lactose broth giving many more false presumptive positive reactions than any of the other media and nearly six times as many as MacConkey broth, which gave the smallest number.All the reactions tended to appear rather more slowly in glucose glutamic acid medium than in the other media.Glucose glutamic acid medium has the advantages of being a chemically defined medium and of not containing any substances which are likely to be inhibitory to coliform organisms. Other glutamic acid media may be found on further investigation to give better results than the present glucose glutamic acid medium, but those presented here suggest that media containing glutamic acid are worthy of further investigation.I am indebted to Dr Ian Sutherland of the M.R.C. Statistical Research Unit for statistical advice and to Dr R. D. Gray of the Public Health Laboratory, Newport (Mon.) and to Dr A. H. Tomlinson of the Public Health Laboratory, Oxford, for much helpful criticism.