Impedance as an alternative to MPN enumeration of coliforms in pasteurized milks

Samples (900) of pasteurized whole, semi-skimmed and skimmed milk were subjected to conventional enumeration of coliforms by a nine-tube most probable number (MPN) technique, and impedance enumeration, in parallel. Regression analysis of the positive samples (98) showed that impedance enumeration was at least as accurate as the MPN method but results were obtained faster, with all testing being completed in 20 h, rather than 48 h. Consumable requirements, and staffing levels, were also much less with the impedance system. The impedance method could therefore beneficially replace the conventional method.