Comparison of three different media for the detection of E. coli and coliforms in water.

The European Drinking Water Directive defines reference methods for the enumeration of microbiological parameters in drinking water. The method to be used for Escherichia coli and coliforms is the membrane filtration technique on Lactose TTC agar with Tergitol 7. Many technical drawbacks of the procedure, as well as its limitations regarding the recent taxonomy of coliforms, make it necessary to evaluate alternative methods. Two alternative assays, a chromogenic media (m-ColiBlu24) and a defined substrate technology-DST test (Colilert 18/Quanty Tray) were compared with the ISO standard with attention to the phenotypic characteristic of the isolates. Results showed that the ISO method failed to detect an important percentage of coliforms and E. coli while m-ColiBlu24 and Colilert 18 provided results in a shorter time allowing the simultaneous detection of E. coli and coliforms with no further confirmation steps.