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

Abstract

The viability of multi-strain cocktails of geneticallymarked strains of Listeriamonocytogenes and Shigatoxin-producing Escherichiacoli (STEC) wereseparately monitored on slices of one brand of a commercially-producedbresaola (ca. pH 6.7 and aw 0.899) during extendedrefrigerated storage. Two slices (ca. 8 g each; ca. 10.2 cm wide, ca. 11 cmlong) of bresaola were layered horizontally within a nylon-polyethylene bag.The outer surface of each slice was inoculated (50 µL total; ca. 3.5 logCFU/package)with a rifampicin-resistant (100 mg/ml)cocktail of either L.monocytogenes (fivestrains) or STEC (eight strains). Bags were vacuum-sealed and then stored at 4°or 10°C for 180 or 90 days, respectively. In each of five trials, three bagswere analyzed for pathogen presence at each sampling interval via the USDA-ARSpackage rinse method. In general, levels of L. monocytogenes and STEC decreased by 3.0and 2.4log CFU/package, respectively, after 180 days when bresaola was stored at 4°C.When bresaola was stored at 10°C for 90 days, levels of L. monocytogenes and STEC decreased by 2.4 and 3.1log CFU/package, respectively. Thus, the (brand of) sliced bresaola evaluatedherein did not provide a favorable environment for either persistence oroutgrowth of surface-inoculated cells of L. monocytogenes or STEC.