Al. Edmiston et Sm. Russell, Evaluation of a conductance method for enumerating Escherichia coli on chicken, pork, fish, beef, and milk, J FOOD PROT, 62(11), 1999, pp. 1260-1265
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.