Monitoring faecal contamination of the Thames estuary using a semiautomated early warning system

The Colifast Early Warning System, based on measuring beta-galactosidase activity (2 h method), was evaluated for monitoring the level of faecal contamination in the upper tidal Thames. Two trials were performed, one following heavy rain in November 2000, the next during a dry and sunny period in July 2001. In general the beta-galactosidase activity and the two coliform reference methods (recovery following membrane filtration with membrane lauryl sulphate broth (MLSB) and Colilert Quantitray) were comparable. However, in several samples in July the beta-galactosidase activity seemed to overestimate the number of culturable coliforms, suggesting that the rapid enzymatic method detected beta-galactosidase produced by other bacterial sources, such as Aeromonas spp. or Vibrio spp., or nonculturable coliforms. The later could be attributed to sunlight-induced injury. Nevertheless, the rapid method based on beta-galactosidase activity gave an estimate of the level of culturable coliforms, which did not differ from both coliform reference methods by more than one log. Monitoring of beta-galactosidase activity in river water samples using the Colifast Analyser may therefore be useful as an early warning indicator of faecal contamination.