DETECTION OF ESCHERICHIA-COLI IN POTABLE WATER USING INDIRECT IMPEDANCE TECHNOLOGY

An indirect impedance technique using membrane lauryl sulphate broth h as been developed and compared with a defined substrate medium (Colile rt, IDEXX) for the detection of Escherichia coli in water. Indirect im pedance gave a 93.3% agreement with Colilert(R) (MPN) with a detection time for the complete development of the Escherichia coli growth sign al of 15 h to detect a single Escherichia coli which is quicker than e ither conventional membrane filtration (minimum 42 h) and currently av ailable defined substrate media(18-24 h). The indirect impedance MLSB method was screened against a range of other bacterial species associa ted with water and only two bacteria (Salmonella arizonae and Salmonel la poona) gave strong signals, both distinguishable from that associat ed with Escherichia coli. Potentially, indirect impedance offers some advantages over currently available technologies for the detection of Escherichia coli in water and food samples. With the impedance method the need for confirmation is removed, it was also found to be more rap id than Colilert(R) and it is possible for the method to be used with samples containing high solids/low volume where membrane filtration wo uld be inappropriate.