ARS | Publication request: Translocation and thermal inactivation of Shiga-toxin producing Escherichia coli in non-intact beef

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 24, 2009
Publication Date: March 25, 2009
Citation: Luchansky,J.,Huang,L.,Sommers,C.,Shoyer,B.,Call,J.,Porto-Fett,A. 2009. Translocation and thermal inactivation of Shiga-toxin producing Escherichia coli in non-intact beef [abstract].ProSafe Beef Conference.Dublin,Ireland.p.1.

Technical Abstract: We compared translocation of genetically-marked strains of serotype O157:H7 Escherichia coli (ECOH) to non-O157:H7 Shiga-Toxin producing Escherichia coli (STEC) following blade tenderization of beef subprimals and the subsequent lethality of these pathogens following cooking of steaks prepared from tenderized subprimals. In Phase I, subprimals were inoculated on the lean side to a target level of ca. 6.0 log CFU/g and then passed once through a mechanical blade-tenderizer with the lean side facing upwards. Ten core samples were removed from each subprimal and cut into six consecutive segments starting from the inoculated side: segments 1 to 4 comprised the top four cm and segments 5 and 6 comprised the deepest four cm. Ten cores were also obtained from control (inoculated, non-tenderized) subprimals, but only the topmost 1 cm (segment 1) was sampled. Each segment was macerated, and the resulting fluid was surface-plated onto Sorbitol-MacConkey plus kanamycin (10 mg/ml; SMACk) for STEC or plus rifampicin (10 mg/ml; SMACR) for ECOH. Levels of STEC and ECOH recovered from segment 1 were 5.26 and 5.96 log CFU/g, respectively, for the control subprimals and 4.99 and 5.74 log CFU/g, respectively, for tenderized subprimals. In Phase II, lean side inoculated and single-pass tenderized subprimals were cut into 1.5 inch thick steaks that were subsequently cooked on a commercial gas grill to internal temperatures ranging from 120 degree to 160 degree F. In general, STEC were more recalcitrant to heat than ECOH at less than 140 degree F. Over the range of temperatures tested, we observed about a 2.5 to 5.0 and 4 to 4.5 log CFU/g reduction of STEC and ECOH, respectively. These results confirm that blade tenderization transfers the majority of E. coli cells into the topmost 1 cm of non-intact beef suprimals. Our data also establish that cooking results in an appreciable reduction of these pathogens that may become internalized into whole muscle cuts of meat via mechanical tenderization.