Fate of Listeria monocytogenes and Shiga Toxin-Producing Escherichia coli on Bresaola Slices During Storage

Abstract

The viability of multistrain cocktails of genetically marked strains of Listeria monocytogenes and Shiga toxin-producing Escherichia coli (STEC) were separately monitored on slices of one brand of a commercially produced bresaola (ca. pH 6.7 and aw 0.899) during extended storage at refrigeration and abusive temperatures. Two slices (ca. 8 g each; ca.10.2 cm wide, ca. 11 cm long) of bresaola were layered horizontally within a nylon-polyethylene bag. The outer surface of each slice was inoculated (50μL total; ca. 3.5 log colony-forming units [CFU]/package) with a rifampicin-resistant (100μg/mL) cocktail of either L. monocytogenes (5 strains) or STEC (8 strains). Bags were vacuum-sealed and then stored at 4°C or 10°C for 180 or 90 d, respectively. In each of 5 trials, 3 bags were analyzed for pathogen presence at each sampling interval via the US Department of Agriculture–Agricultural Research Service package rinse method. In general, levels of L. monocytogenes and STEC decreased by 3.0 and 2.4 log CFU/package, respectively, after 180 d when bresaola was stored at 4°C. When bresaola was stored at 10°C for 90 d, levels of L. monocytogenes and STEC decreased by 2.4 and 3.1 log CFU/package, respectively. Thus, the sliced bresaola evaluated herein did not provide a favorable environment for either persistence or outgrowth of surface-inoculated cells of L. monocytogenes or STEC.