Modeling Surface Transfer of Listeria monocytogenes on Salami during Slicing

Abstract

Listeria monocytogenes has been implicated in several listeriosis outbreaks linked to the consump tion of presliced ready-to-eat (RTE) deli meats, which has drawn considerable attention in regard to possible cross-contamination during slicing operation at retail and food service environments. Salami with 15% fat (a moderate l fat content deli item) was used to investigate the transfer of L. monocytogenes between a meat slicer and salami slices and to understand its impact on food safety. A 6-strain cocktail of L. monocytogenes was inoculated onto a slicer blade to an initial level of approximately 3, 5, 6, 7, or 9 log CFU/blade (or approximately 2, 4, 5, 6, or 8 log CFU/cm2 of the blade edge area), and then the salami was sliced to a thickness of 1 to 2 mm (case I). For another cross-contamination scenario, a clean blade was first used to slice salami loaf that was previously surface-inoculated with L. monocytogenes (approximately 3, 5, 6, 7, 8, or 9 log CFU/100 cm2 area), followed by slicing the uninoculated salami loaf (case II). The salami slicing rate was maintained at an average of 3 to 4 slices per minute in all the tests. The results showed that the empirical models developed in this study were reasonably accurate in describing the transfer trend/pattern of L. monocytogenes between the blade and salami slices if the inoculum level was >5 log CFU on the salami or blade. With an initial inoculum at 3 or 4 log CFU, the experimental data seemed to suggest a rather random pattern of bacterial transfer between blade and salami. The currently developed models are microbial load (n), sequential slice index (X), and contamination route dependent, which might limit their applications to certain conditions. However, the models may be further applied to predict the 3 or 4 log CFU level (and below) cross-contamination of salami slicing process. Considering only few data are available in the literature regarding food pathogen surface transfer, the empirical models may provide a useful tool in building risk assessment procedures.