Evaluation of Enterolert®for the enumeration of enterococci in the marine environment

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Abstract
Current methods for the analyses of enterococcal densities include the membrane filtration (MF) technique and the multiple tube fermentation technique for the most probable number (MPN). Both techniques are labour intensive, tedious, and require a minimum of 48–72 h before results can be obtained. The Enterolert® system, designed to detect enterococci in water in 24 h, uses 4‐methylumbelliferyl‐ß‐D‐glucoside as a defined substrate nutrient indicator. This compound, when hydrolysed by enterococcal‐ß‐glucosidase, releases 4‐methylumbelliferone which exhibits fluorescence under a UV365 lamp. In this study 343 marine water samples from selected sites in the Wellington area of New Zealand were tested to evaluate the sensitivity and specificity of Enterolert in parallel with the MF method. Statistical analysis of parallel test results showed a strong linear correlation (r = 0.927) and no significant difference between the two methods by paired Mest analysis (P = 0.39). Based on the 2.4% false positive and 0.3% false negative rates, Enterolert was found to have a sensitivity of 99.8% and a specificity of 97.0%. Activity‐costing analyses revealed that the variable cost per test was less for Enterolert (NZ$18.33) than MF (NZ$22.79). Significant time savings are achieved because Enterolert requires less time than MF for reagent preparation, sample set‐up, incubation, and reading of tests. The results from this study suggest that more widespread use of this new technology in marine water quality monitoring is warranted, since rapid tests mean that monitoring agencies can respond to sudden increases in enterococci numbers more quickly and can therefore take immediate corrective action to ensure the safety of users of recreational waters.