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Cross-contamination Between Slicers and Deli Foods

November 2013

Slicers are commonly used in the deli department of retail food stores and have been known for many years to serve as vehicles for cross-contaminating deli foods with foodborne pathogens. Outbreaks of Listeria monocytogenes, Salmonella, and Escherichia coli O157:H7 infections have been linked to consumption of deli foods, and cross-contamination by these pathogens during slicing has been suspected as the mode of transmission.

The risk of cross-contamination of foods can be enhanced by contact with contaminated slicer surfaces. Routine proper cleaning and sanitizing procedures are widely thought to be effective in preventing cross-contamination but failure to disinfect can occur due to poor training of employees. Some surfaces of slicing equipment are difficult to clean, thereby increasing the probability that foodborne pathogens may not be removed during routine cleaning and sanitizing.

Quaternary ammonium-based solutions are commonly used to sanitize slicers but their efficacy in killing foodborne pathogens is generally reduced in commercial settings when organic matter is present. Hence, it would be beneficial to use a sanitizer that retains disinfectant activity in the presence of organic matter. A bactericide containing levulinic acid (LA) plus sodium dodecyl sulfate (SDS) has been determined in our laboratory to be an effective sanitizer in the presence of chicken feces, feathers, and feed.

The objectives of this research were to determine the degree to which cross-contamination with L. monocytogenes, S. Typhimurium, and E. coli O157:H7 can occur between surfaces of deli slicers and foods, and the efficacy of LA plus SDS in inactivating these pathogens on slicers.

Five-strain mixtures of each pathogen were separately surface-inoculated on ham, roast beef, and cheese (ca. 3.0 log CFU/cm2), followed by slicing the foods and analyzing five slicer surface locations (meat grip, carriage tray, gauge plate, slicer blade, and blade cover) for cross-contamination (Study 1). In a second study, slicer blades inoculated with each pathogen (ca. 8.5 log CFU/blade) were used to slice the same food several times, followed by analysis of each slice for cross-contamination. The transfer rates of pathogens to slicer surfaces (Study 1) and to foods (Study 2) were determined.

In Study 1, test pathogens were recovered from the five food-contact locations on slicers, with significantly (P < 0.05) less recovery from blades than from other locations. In the second study, the number of CFUs of the three pathogens transferred from blades to foods decreased logarithmically (R2 > 0.9) as the number of slices progressed.

Sanitizers applied as liquids or foams at three concentrations (0.5% LA + 0.05% SDS, 1% LA + 0.1% SDS, and 2% LA + 0.5% SDS) were tested for efficacy in decontaminating slicer blades at 21°C. Spraying contaminated blades with 1% LA plus 0.1% SDS as a foam (45 to 55 psi) was the most efficacious of all treatments tested, reducing the three pathogens by 6.0 to 8.0 log CFU/blade within 1 min.

This study determined the dynamics of cross-contamination of L. monocytogenes, S. Typhimurium, and E. coli O157:H7 from contaminated deli foods to slicers and from contaminated slicers to deli foods. After slicing surface-inoculated foods, pathogens were recovered from five contact surfaces on slicers, with significantly (P < 0.05) less transfer to the blades than to meat grips and carriage trays. At an initial inoculum of ca. 8.5 log CFU/blade, the transfer of pathogens decreased logarithmically from an initial count of 4.0 log CFU/slice to <1.5 log CFU on the sixtieth slice. Treatment of blades with a mixture of levulinic acid (1%) plus SDS (0.1%) as a foam reduces the three pathogens by at least 6 log CFU/blade within 1 min. This combination of chemicals also may have potential for use as an effective sanitizer for large-scale applications in food processing facilities.