Evaluation of Enterolert (R) for the enumeration of enterococci in the marine environment

Current methods for the analyses of enterococcal densities include the memb rane 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. T he Enterolert(R) system, designed to detect enterococci in water in 24 h, u ses 4-methylumbelliferyl-beta-D-glucoside as a defined substrate nutrient i ndicator. This compound, when hydrolysed by enterococcal-beta-glucosidase, releases 4-methylumbelliferone which exhibits fluorescence under a UV365 la mp. In this study 343 marine water samples from selected sites in the Welli ngton area of New Zealand were tested to evaluate the sensitivity and speci ficity of Enterolert in parallel with the MF method. Statistical analysis o f parallel test results showed a strong linear correlation (r = 0.927) and no significant difference between the two methods by paired t-test 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 w as less for Enterolert (NZ$18.33) than MF (NZ$22.79). Significant time savi ngs are achieved because Enterolert requires less time than MF for reagent preparation, sample set-up, incubation, and reading of tests. The results f rom this study suggest that more widespread use of this new technology in m arine water quality monitoring is warranted, since rapid tests mean that mo nitoring agencies can respond to sudden increases in enterococci numbers mo re quickly and can therefore take immediate corrective action to ensure the safety of users of recreational waters.