Article révisé par les pairs
Résumé : Faecal coliforms (FC) and Escherichia coli enumeration is classically used to monitor the microbiological quality of surface waters. Traditionally, the methods used for the enumeration of these indicator bacteria are culture-based (in liquid or on solid culture media) requiring long incubation times; this makes them unable to rapidly detect faecal pollution. ln this study, an early warning method to detect faecal contamination of river waters was investigated. This method is based on the measurement of the BETA-D-glucuronidase (an enzyme specifie of E. coli) activity (GLUase activity) without any cultivation step using the substrate 4-methylumbelliferyl-BETA-D-glu¬curonide (MUG). The GLUase activity measurement can be performed within 30 min. Significant linear regressions in log-log plots between the glucuronidase (GLUase) activity and, on one hand, FC number estimated by plate count and, on the other hand, E. coli abundance evaluated by the most probable number microplate method were found during the present study. Based on experimentally determined regressions, FC and E. coli abundance were calculated from GLUase activity data. The use of this early warning method was first pos¬itively tested to evaluate the microbiological qua lit y in raw water of a drinking water treatment plant located in an urban area. The method proved to be able to rapidly and accurately estimate the spatial distribution of the microbiological contamination in a large river. Due to its rapidity, reproducibility (better than that of the culture-based methods) and relatively low cost, the GLUase activity measurement appears to be a very useful tool for the monitoring of microbiological pollution in freshwaters.