Title: Translocation and thermal inactivation of Escherichia coli O157:H7 in beef steaks Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 7, 2008
Publication Date: September 1, 2008
Citation: Luchansky, J.B., Call, J.E. 2008. Translocation and thermal inactivation of Escherichia coli O157:H7 in beef steaks. Meeting Abstract. Annual Meeting of Food Micro in Aberdeen, Scotland. P0639. Technical Abstract: We quantified the translocation of Escherichia coli O157:H7 from the surface into the interior of a beef subprimal following blade tenderization and the subsequent lethality of the pathonge following cooking of steaks prepared from the tenderized subprimals. In Phase I, subprimals were inoculated on the lean side with ca. 4.0 log10 CFU/g of a five-strain mixture of E. coli O157:H7 and then passed once through a mechanical blade-tenderizer with the lean side facing upwards. A second set of inoculated subprimals that were not tenderized served as positive controls. Six core samples (ca. 10 cm long and ca. 5 cm in diameter) 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 of the core sample and segments 5 and 6 comprised the deepest four cm. Six cores were also obtained from control subprimals, but only the top 1 cm (segment 1) of each was sampled. Each segment (ca. 8 g each for segments 1-4 and ca. 16 g each for segments 5 and 6) was macerated, and the resulting fluid was surface-plated onto Sorbitol-MaConkey plus rifampicin agar plates. The levels of E. coli recovered by direct plating from the surface of each core sample, that being segment 1, when inoculated with ca. 4.0 log10/g were 3.19 log10 CFU/g for the non-tenderized controls subprimals and 3.40 log10 CFU/g from subprimals that were tenderized. The levels recovered in segment 2 were 7-to-34-fold lower than levels recovered from segment 1, and it was possible to recover E. coli from all six segments from subprimal cores that received an initial inoculation of 3.19 log10 CFU/g. In Phase II, lean side inoculated, single-pass tenderized subprimals were cut by hand into 0.75, 1.0, and 1.25 inch thick steaks that were subsequently cooked on an open-flame gas grill to internal instantaneous temperatures ranging from 120 to 140F. The steaks were removed from the grill at the target temperature, placed in a bag, and immediately chilled in a ice water bath. Each steak was cut into seven separate portions that were separately weighed and subsequently macerated. The resulting fluid was surface plated onto SMAC agar plates. In general, regardless of temperature or steak thickness, depending on the portion, we observed about a 1.5- to 3.0-log reduction in pathogen numbers following cooking. These results validate that mechanical blade tenderization can transfer E. coli O157:H7 into the deeper tissues of subprimals, with the vast majority of the cells remaining in the top one cm. In addition, cooking on a commercial-style gas grill is effective at eliminating cells of the pathogen that may be distributed throughout a steak that was blade-tenderized.