Use of a commercial gene probe assay kit for rapid MPN enumeration of Escherichia coli in drinking water

A commercial gene probe assay kit for presence/absence determination of Escherichia coli in food samples has been used in the standard UK six tube format most probable number (MPN) method for enumerating E. coli in drinking water samples. Presence/absence analysis with the gene probe kit (requiring 3 h) of all MPN tubes after a 21–24 h incubation (minerals modified glutamate; 37°C) enumerated confirmed E. coli in 24–27 h which offered an improvement of up to 48 h over the standard UK MPN method. MPNs determined by the gene probe method and the standard UK method agreed in nine of the 16 water samples which were analysed and for which E. coli concentrations were within the detection limits of the six tube MPN format. This was consistent with the gene probe method detecting one E. coli in a tube. For the other seven water samples, the gene probe method registered positive only 20 of the 30 tubes which the standard UK method determined to be positive. The sensitivity of the gene probe method for drinking water samples, although encouraging, needs improvement perhaps through kit quality control procedures.