Comparison of membrane filtration and Autoanalysis Colilert presence-absence techniques for analysis of total coliforms and Escherichia coli in drinking water samples

Abstract

Over a 4-month period, 950 samples of treated drinking water were analyzed for total coliforms (TC) and Escherichia coli by both membrane filtration (MF) and Autoanalysis Colilert presence-absence (AC) techniques. The two tests agreed 97% of the time on the basis of presumptive TC results and 98.5% of the time on the basis of verified TC results. Samples which produced disagreement between the two tests were most often TC positive by MF and TC negative by AC. E. coli was recovered four times: twice by MF only, and twice by AC only but without the diagnostic fluorescence reaction. In two samples, E. coli could not be isolated from fluorescence-positive AC tests. On the basis of these results, the AC test was implemented as the routine analytical procedure for TC but not for E. coli.