An Evaluation of a Conductance Method for the Enumeration of Enterobacteriaceae in Milk

Abstract

A method for the quantitative detection of Enterobacteriaceae in raw milk utilizing automated, conductance monitoring of a selective medium was studied. The levels of pure Enterobacteriaceae cultures as well as Enterobacteriaceae levels in naturally contaminated raw milk were accurately measured using the conductance method when statistically compared to results obtained by an agar plating method. The correlation coefficient (r-value) for naturally contaminated raw milk samples was 0.92. Using a pass/fail limit of 100 CFU/ml, additional raw milk samples were analyzed and 90% of these samples were correctly classified into the correct pass/fail group using the results of the conductance monitoring method. Enterobacteriaceae were detected in raw milk at levels of <10 – 500 CFU/ml in 12 - 6 hours, respectively, using the conductance method.