Transfer of Listeria monocytogenes during Mechanical Slicing of Turkey Breast, Bologna, and Salami

Abstract

A commercial delicatessen slicer was used as the vector for sequential quantitative transfer of Listeria monocytogenes (i) from an inoculated slicer blade (∼108, 105, or 103 CFU per blade) to 30 slices of uninoculated delicatessen turkey, bologna, and salami, (ii) from inoculated product (∼108 CFU/cm2) to the slicer, and (iii) from inoculated product (108, 105, or 103 CFU/cm2) to 30 slices of uninoculated product via the slicer blade. Cutting force and product composition also were assessed for their impact on L. monocytogenes transfer. Five product contact areas on the slicer, which were identified from residue of product bathed in Glow-Germ, were also sampled using a 1-ply composite tissue technique after inoculated product had been sliced. After being sliced with inoculated blades, each product slice was surface or pour plated on modified Oxford agar and/or enriched in University of Vermont medium. Greater transfer (P < 0.05) occurred from inoculated turkey (108 CFU/cm2) to the five slicer contact areas from an application force of 4.5 kg as compared with 0 kg. On uninoculated product sliced with blades inoculated at 108 CFU per blade, L. monocytogenes populations decreased logarithmically to 102 CFU per slice after 30 slices. Findings for the inoculated slicer blade and product (105 CFU per blade or cm2) were similar; L. monocytogenes concentrations were 102 CFU per slice after 5 slices and enriched samples were generally negative for L. monocytogenes after 27 slices. For uninoculated product sliced with blades inoculated at 103 CFU per blade, the first 5 slices typically produced L. monocytogenes at ∼10 CFU per slice by direct plating, and enrichments were negative for L. monocytogenes after 15 slices. The higher fat and lower moisture content of salami compared with turkey and bologna resulted in a visible fat layer on the blade that likely prolonged L. monocytogenes transfer. As a result of cross-contamination, those delicatessen-sliced meats that allow growth of L. monocytogenes during prolonged refrigerated storage likely pose an increased public health risk for certain consumers.