Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2013
Publication Date: 6/26/2013
Citation: Luchansky, J.B., Porto Fett, A.C., Shoyer, B.A., Phillips, J.G., Eblen, D., Evans, P., Bauer, N. 2013. Thermal inactivation of shiga toxin-producing 0157:H7 and non-0157-H7 cells of Escherichia coli within wafers of ground beef. Journal of Food Protection. 76:1434-1437. Interpretive Summary: Escherichia coli O157:H7 and six related “serotypes” of E. coli can cause serious illness in humans and are considered adulterants in ground beef. While a great deal of information is available on the ability of cooking (heat) to kill E. coli O157:H7 in ground beef there is very little information available on the heat resistance of these other serotypes of E. coli. In this study the heat resistance of E. coli O157:H7 and these other serotypes was determined in a laboratory scale model system that used thin wafers of ground beef. The heat resistance of E.coli O157:H7 and the other serotypes were found to be similar. Additional studies will now be conducted using ground beef patties on actual commercial gas and electric grills. This data will assist the food industry and consumers by providing the cooking information needed to prevent illnesses caused by these harmful bacteria.
Technical Abstract: We quantified the effect of heat on a single strain of E. coli serotypes O111:H-, O45:H2, O103:H2, O121:H19, O145:NM, O26:H11, and O157:H7 in a model beef system. For each of two trials, freshly-ground beef of higher (70:30 = percent lean:fat) or lower (93:7 = percent lean:fat) fat content was separately inoculated with each strain to ca. 7.0 log CFU/g. Next, ca. 3-g samples of inoculated beef were transferred into sterile filter bags and with the aid of a stainless-steel roller, the meat was flattened (ca. 1.0 mm thick) within the bags and then vacuum-sealed. For each temperature and time point, three bags of these inoculated wafers of beef were submerged in a thermostatically-controlled water bath and heated to an internal temperature of 54.4 deg C (130 deg F) for up to 90 min, or to 60 deg C (140 deg F) for up to 4 min, or to 65.6 deg C (150 deg F) for up to 0.27 min. In lower fat wafers, D-values ranged from 13.5 to 23.7 min, 0.7 to 1.2 min, and 0.05 to 0.08 min at 54.4, 60, and 65.6 deg C, respectively, whereas heating higher fat wafers to 54.4, 60, or 65.6C generated D-values of 20.2 to 32.6 min, 0.7 to 1.1 min, and 0.05 to 0.2 min, respectively. In addition, we observed log CFU/gram reductions of ca. 2.7 to 6.7 log CFU/gram at 54.4 deg C after 90 minutes, ca. 3.3 to 6.0 log CFU/gram at 60.0 deg C for 4 minutes, and 1.5 to 5.8 log CFU/gram at 65.6 deg C for 0.26 minutes. In general, with the exception of wafers heated to 54.4 deg C, no effect of fat level on lethality and no appreciable differences in thermal inactivation among strains/serotypes were observed. These data established that cooking times/temperatures effective for inactivating serotype O157:H7 strains of E. coli in ground beef are equally effective against the additional six Shiga toxin-producing strains investigated herein.