Cross-contamination between Deli Foods and Slicers by Escherichia coli O157:H7, Listeria monocytogenes and Salmonella, and Validation of the Antimicrobial Efficacy of Sanitizers

Introduction: Foodborne pathogens have been associated with ready-to-eat (RTE) sliced deli meats. Sanitizers are widely used to minimize the risk of cross-contamination in the food industry, but their efficacy can be reduced when used in commercial settings such as on slicers. It has been suggested that levulinic acid plus sodium dodecyl sulfate (SDS) may provide substantial antimicrobial efficacy on food processing equipment.

Purpose: The purpose of this study was to: (1) determine the levels of cross-contamination that can occur between deli foods and slicers contaminated by Escherichia coli O157:H7, Listeria monocytogenes and Salmonella Typhimurium, and (2) determine the killing efficacy of levulinic acid plus SDS for inactivating these three pathogens on slicers.

Methods: E. coli O157:H7, L. monocytogenes and S. Typhimurium were individually surface-inoculated either on deli foods (10^4-5 CFU/cm²) to contaminate slicer surfaces or on slicer blades (10^7-8 CFU/blade) to contaminate deli foods, including beef, cheese and ham. The populations of pathogens on food slices and at 6 contact locations on slicers were enumerated. After application of sanitizers, either as a liquid or as foam, surfaces of the slicers were swabbed for pathogen enumeration.

Results: The three pathogens survived on the dried surface of slicers for at least 6 days. After slicing 5 to 10 slices, up to 10³ CFU of pathogens/cm² from the contaminated deli foods (10^4-5 CFU/cm²) were transferred to slicer surfaces, including the grip, carriage tray, blade cover, blade and gauge plate.  Once the slicer blades were contaminated by E. coli O157:H7, L. monocytogenes or S. Typhimurium, these pathogens were transferred at a rate of 10^1-3 CFU per slice to up to 100 slices.  Contaminated slicer surfaces sprayed with a sanitizer containing 1% levulinic acid plus 0.1% SDS as a foam (45-55 psi) reduced 10^6-8 CFU of pathogens/blade, including E. coli O157:H7, L. monocytogenes and S. Typhimurium within 1 min at 21°C.

Significance: Results revealed that pathogen cross-contamination can occur between slicer and deli foods and that levulinic acid plus SDS sanitizer can effectively reduce foodborne pathogen populations of 10^6-8 CFU/blade on slicers.