[Experiences with the detection of E. coli and coliform bacteria with reference to the drinking water regulation of...

After the introduction of a limiting value for coliform bacteria in the German Drinking Water Regulation from May 22, 1986 the detection of coliform bacteria has become as important as that of E. coli to indicate pathogenic Enterobacteriaceae and fecal contamination. 130 water samples from different steps of drinking water treatment and distribution have been investigated for Enterobacteriaceae, even when typical indicating marks for such as acid- and gas-formation in the enrichment media were absent. We found the total of 46 isolates of Enterobacteriaceae, among which E. coli was the most frequent one. Whereas in 7 samples with acid- and gas-formation in the enrichment media Enterobacteriaceae could not be isolated, coliform bacteria and other enterobacteriaceae were found in 6 samples without these characteristics. As our experiences have show, those 'false positive' results can be avoided by a careful identification procedure of isolated microorganisms. The hygienically much more important 'false negative' results would not be recognized in routine control of drinking water following the prescribed methods.