Al. Edmiston et Sm. Russell, Specificity of a conductance assay for enumeration of Escherichia coli from broiler carcass rinse samples containing genetically similar species, J FOOD PROT, 63(2), 2000, pp. 264-267
Experiments were conducted to evaluate the specificity of a rapid method fo
r enumeration of Escherichia coti from fresh broiler chicken carcasses. In
three separate trials, E. coli, Citrobacter freundii, Salmonella Enteritidi
s, and Shigella sonnei were serially diluted and then inoculated into ident
ical broiler chicken carcass rinses. Inoculated rinses were mixed with doub
le-strength Coliform Medium supplemented with 2% dextrose. This mixture was
placed in a Bactometer module in duplicate, and conductance was measured a
t 44 degrees C. Results indicated that C. freundii did not grow to an appre
ciable degree in the selective medium at 44 degrees C. Salmonella Enteritid
is grew similarly to E. coli; however, an initial level of 10(6) Salmonella
in the food product would be required for Salmonella to interfere with enu
meration of E. coli using this method. S. sonnei grew at a more rapid rate
than E, coli; however, there was an interaction between the regression line
s formed when serial dilutions (log(10) CFU/ml) were compared to E. coli de
tection times for these two species of bacteria. Therefore, high levels of
S. sonnei in a food sample may interfere with the enumeration of E. coli. I
n general, Salmonella and Shigella are not found at high enough levels on p
oultry products to interfere with enumeration of E. coli using this method
and, if found at high levels, would be detected and rejected using this pro
cedure. Hence, the presence of organisms that are genetically and phylogene
tically similar to E. coli would not preclude enumeration of E. coli using
conductance under these conditions.