| Summary: | The purpose of this study was to evaluate the antimicrobial efficacy of an aqueous ozone (Bio-Safe) treatment and lactic acid solutions on natural microbiota and <i>E. coli</i> O157:H7 and Salmonella surrogates on beef carcasses and trim in a commercial beef processing plant. For every repetition, 40 carcass and 40 trim swabs (500 cm<sup>2</sup>) were collected. Samples were taken using EZ-Reach<sup>TM</sup> swabs, and plated into aerobic plate count (APC), coliform, and <i>E. coli</i> Petrifilm<sup>TM</sup> for enumeration. In addition, a five-strain cocktail (MP-26) of <i>E. coli</i> surrogates was inoculated onto trim. For every trim surrogate repetition, 30 trim pieces were sampled after attachment and after ozone intervention. Samples were diluted and counts were determined using the TEMPO<sup>®</sup> system for <i>E. coli</i> enumeration. Ozone and lactic acid interventions significantly reduced (<i>p</i> < 0.003) bacterial counts in carcasses and trim samples. Moreover, lactic acid further reduced APC and coliforms in trim samples compared to ozone intervention (<i>p</i> < 0.009). In the surrogate trials, ozone significantly reduced (<i>p</i> < 0.001) surrogate concentration. Historical data from the plant revealed a reduction (<i>p</i> < 0.001) of presumptive <i>E. coli</i> O157:H7 in trim after a full year of ozone intervention implementation. The novel technology for ozone generation and application as an antimicrobial can become an alternative option that may also act synergistically with existing interventions, minimizing the risk of pathogens such as Salmonella and <i>E. coli</i> O157:H7.
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