Detection of Escherichia coli in potable water using direct impedance technology

An indirect impedance technique using membrane lauryl sulphate broth has been developed and compared with a defined substrate medium (Colilert, IDEXX) for the detection of Escherichia coli in water. Indirect impedance gave a 93.3% agreement with ColilertB (MPN) with a detection time for the complete development of the Escherichia coli growth signal of 1.5 h to detect a single Escherichia coli which is quicker than either conventional membrane filtration (minimum 42 h) and currently available delined substrate media (18-24 h). The indirect impedance MLSB method was screened against a range of other bacterial species associated with water and only two bacteria (Salmonella arizonae and Salmonella poona) gave strong signals, both distinguishable from that associated 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 rapid than Colilert@ and it is possible for the method to be used with samples containing high solids/low volume where membrane filtration would be inappropriate.