Fate of Inoculated Escherichia coli O157:H7, Cultured under Different Conditions, on Fresh and Decontaminated Beef Transitioned from Vacuum to Aerobic Packaging

Abstract

This study evaluated the behavior of Escherichia coli O157:H7 during aerobic storage, after storage in vacuum packages, on beef inoculated with cultures prepared (35°C, 24 h) in tryptic soy broth without dextrose (TSB), nonacid hot water carcass decontamination runoff fluids (washings; pH 6.0; WASH), cells from biofilms formed on stainless steel coupons in WASH (WETB), or WETB dried (25°C, 12 h) before harvesting of cells (DRYB). These inocula were applied to fresh beef pieces (40 cm2), which were then left untreated or treated by immersion in hot water (75°C) followed by 2% lactic acid (55°C; hot water/lactic acid [HW/LA]), for 30 s each. Inoculated samples were vacuum packaged and stored at 0 (30, 60, or 90 days), 4 (7 or 14 days), or 12°C (4 or 8 days) and subsequently transferred to retail packages for aerobic storage at 7°C for 5 days. Populations of E. coli O157:H7, regardless of inoculum type, remained generally unchanged (P > 0.05) after aerobic storage (7°C, 5 days) of untreated or HW/LA-treated beef samples previously stored in vacuum packages at 0 or 4°C. However, reductions in E. coli O157:H7 levels were generally obtained when vacuum packaged, untreated beef samples previously stored at 12°C were transitioned to aerobic conditions. Additionally, despite similar (P > 0.05) levels of E. coli O157:H7 cells of TSB, WASH, WETB, and DRYB origin on vacuum-packaged, untreated samples after 8 days of storage at 12°C, subsequent aerobic storage resulted in larger (P <0.05) reductions of cells of WETB and DRYB origin than for cells of TSB and WASH origin. For HW/LA-treated beef previously stored at 12°C in vacuum packages, populations of E. coli O157:H7 remained largely unchanged after aerobic storage in retail packages. Results thus indicated that aerobic storage of beef (7°C, 5 days) previously stored in vacuum packages at 0 or 4°C did not lead to E. coli O157:H7 population changes, whereas transition from vacuum packages stored under mildly abusive temperature (12°C) to aerobic storage may have caused injury and death to the pathogen.