Comparison of a novel ColiPlateTM kit and the standard membrane filter technique for enumerating total coliforms andEscherichia coli bacteria in water

The new ColiPlate (CP) kit was evaluated comparatively with the standard membrane filter (MF) technique for enumerating total coliforms and Escherichia coli in water. In testing natural water samples, good correlations were observed for enumerating total coliforms (R2=0.84) and E. coli (R2=0.95). However, counts of E. coli population density estimated by CP were 47% higher than counts estimated by MF. With the water samples spiked with culture-grown E. coli cells, the correlation between the methods was strong for both total coliforms (R2=0.95) and for E. coli (R2=0.94). E. coli densities were estimated to be 20% higher using CP compared with MF. Samples spiked with rehydrated freeze-dried E. coli cells (with high portion of injured or weakened cells) showed a strong correlation between the two methods (R2=0.93, for either total coliforms or E.coli). However, estimated total coliforms and E. coli densities were higher by CP than MF counts (38 and 168%, respectively). The CP test is therefore considered a more reliable method than the traditional MF for enumerating E. coli in samples with high levels of injured or weakened cells.