Effects of steam-vacuuming and hot water spray wash on the microflora of refrigerated beef carcass surface tissue inoculated with Escherichia coli O157:H7, Listeria innocua, and Clostridium sporogenes

The fates of several bacterial populations on beef carcass surfaces were examined immediately following hot water washes (W) delivered through a beef carcass wash cabinet or application of steam-vacuum (SV). Additionally, the long-range effectiveness of W and SV and several bacterial populations was also determined during storage up to 21 days at 5°C under vacuum-packaged conditions. Fresh, unaltered bovine feces spiked with antibiotic-resistant strains of Escherichia coli O157:H7, Listeria innocua, and Clostridium sporogenes were used to inoculate beef carcass tissue prior to W or SV treatment. All treatments were equally effective as is indicated by bacterial populations immediately following any of the treatments (P > 0.05); however, the combination of SV followed by W consistently produce arithmetically greater bacterial reductions. In general, all treatments produced initial reductions of up to 2.7 log CFU/cm² for APC, lactic and bacteria, and L. innocua, but by 4 days bacterial numbers had increased to levels of at least 7 log CFU/cm². E. coli O157:H7 was initially reduced by as much as 3.4 log CFU/cm² and did not grow to original inoculation levels for the duration of the experiment. Vegetative counts of C. sporogenes were initially reduced by as much as 3.4 log CFU/cm², and numbers continued to decline for the duration of the study. These results indicate that the use of W and SV effectively reduces bacterial populations from beef carcass tissue immediatley after treatment. Additionally, storage of treated tissue up to 21 days at 5°C did not appear to offer any competitive advantage to potentially pathogenic microorganisms.