Evaluation of a conductance method for enumerating Escherichia coli on chicken, pork, fish, beef, and milk

Experiments were conducted to evaluate a rapid method for enumerating Esche richia coli on food products of animal origin. In study I, rinses from samp les of chicken, ground beef, pork, and fish and samples of milk were inocul ated with various levels of actively growing E. coli. Conductance assays we re monitored at 44 degrees C. On each sample using coliform medium suppleme nted with 2% dextrose. High correlations between E. coli concentrations and E. coli conductance detection times (ECDTs) were found (r = -0.97 to -0.99 ) for all foods tested in all replicates; however, in most cases, the conco rdance correlation coefficients (r(c)) were low, indicating a lack of predi ctive accuracy. In this study, low accuracy of the conductance method for e stimating E. coli counts was attributed to use of concentrations of E. coli that exceed 10(6) CFU/mL, the detection threshold of the instrument. Slope s of the linear regression lines (E. coli concentration vs. ECDT) for each type of food tested were not significantly different (P < 0.0001), indicati ng that a single regression equation may be used to estimate E. coli counts for all of the types of food tested in 1 to 7.5 hours using ECDT. In study II, ECDTs for pork, fish, beef, and milk significantly (P < 0.05) decrease d in a linear manner as time of temperature abuse increased. Although the E CDT for chicken decreased linearly, no significant differences were observe d between 3 and 6 or between 9 and 12 h of abuse. These data demonstrate a strong relationship between increasing populations of E. coli due to temper ature abuse and decreasing ECDT. Therefore, results from both studies indic ate that this method could be useful for estimating naturally occurring pop ulations of E. coli on foods of animal origin.