Recovery of Escherichia coli biotype I and Enterococcus spp. during refrigerated storage of beef carcasses inoculated with a fecal slurry

Three beef front quarters/carcasses were inoculated with a slurry of cattle manure. During storage at 4 degrees C, two sponge samples from each of thr ee sites (i.e., 100 cm(2) from each of two fat surfaces and 100 cm(2) from a lean surface) were taken from each of the three carcasses on days 0, I, 3 , 7, and 10 after inoculation. The initial numbers of Escherichia coli aver aged 2.0 log(10) CFU/cm(2) (1.21 to 2.47 log(10) CFU/cm(2)) using the Petri film method and 2.09 log(10) most probable number (MPN)/cm(2) (0.88 to 2.96 log(10) MPN/cm(2)) using the MPN method. The initial numbers of enterococc i averaged 3.34 log(10) CFU/cm(2) (3.07 to 3.79 log(10) CFU/cm(2)) using ka namycin esculin azide agar. In general, an appreciable reduction ht the num bers of E. coti occurred during the first 24 h of storage; for the Petrifil m method an average reduction of 1.37 log(10) CFU/cm(2) (0.69 to 1.71 log(1 0) CFU/cm(2)) was observed, and for the MPN method an average reduction of 1.52 log(10) MPN/cm(2) (0.47 to 2.08 log(10) MPN/cm(2)) was observed. E. co li were not detected (<-0.12 log(10) CFU/cm(2)) using Petrifilm on day 7 of the storage period on two (initial counts of 1.21 and 2.29 log(10) CFU/cm( 2)) of the three carcasses. However, viable E. coli cells were recovered fr om these two carcasses after a 24-h enrichment at 37 degrees C in EC broth. Viable E. call cells were detected at levels of -0.10 log(10) CFU/cm(2) on the third carcass (initial count of 2.47 log(10) CFU/cm(2)) after 7 days a t 4 degrees C. No significant difference in recovery of viable cells was ob served between the MPN and Petrifilm methods on days 0, 1, and 3 (P > 0.05) . However, viable E. coli cells were recovered from all three carcasses by the MPN method on day 7 at an average of -0.29 log(10) MPN/cm(2) (-0.6 to - 0.1 log(10) MPN/cm(2)). On day 10, viable cells were recovered by the MPN m ethod from two of the three carcasses at -0.63 and -0.48 log(10) MPN/cm(2) but were not recovered hom the remaining carcass (<-0.8 log(10) MPN/cm(2)). Similar to E. coli, the greatest reduction (average of 1.26 log(10) CFU/cm (2), range = 1.06 to 1.45 log(10) CFU/cm(2)) in the numbers of enterococci occurred during the first 24 h of storage. Because of higher initial number s and a slightly slower rate of decrease, the numbers of Enterococcus spp. were significantly higher (P < 0.017) than the numbers of E. coli Biotype I after 3, 7, and 10 days of storage. These results suggest that enterococci may be useful as an indicator of fecal contamination of beef carcasses.