Inhibition of Listeria monocytogenes on Deli Slicers and Food Contact Surfaces with Lactic Acid Bacteria

Introduction: Listeria monocytogenes is a pathogen of concern for the food industry given its capacity to withstand standard sanitation regimes, to form biofilms, and to survive and grow in moist, refrigerated environments.

Purpose: To estimate the quantitative reduction of L. monocytogenes on stainless steel surfaces.

Methods: Six deli slicers and twelve unsliced deli meat were procured commercially. Six meat chubs were submerged into a three-strain cocktail of L. monocytogenes at 10⁶ CFU/ml and were air-dried for 30 minutes. Each deli meat chub was sliced separately in a separate slicer. Three of the slicers were sprayed with 10 ml of a cocktail of lactic acid bacteria at a concentration of 10⁹ CFU/ml, and were allowed to air-dry for an hour. The other six uninoculated deli meat chubs were sliced separately in each slicer. The blade and table of each slicer was swabbed with EZ Reach pre-hydrated sterile sponges. All swab samples were plated onto Modified Oxford Listeria Selective Agar. Typical colonies were counted after incubation for 18-24 hours at 35 ± 1 C. The experiment was replicated three times.

Results: The estimated reduction of L. monocytogenes on the slicer’s table was approximately 0.9 log/100 cm². On the other hand, there was not any growth estimated on the blade in both the control and the treatment indicating that the inoculated meat did not transfer any pathogen to the blade as it did the table.

Significance: The use of lactic acid bacteria as a biocontrol method for L. monocytogenes may help reduce the burden of this pathogen in the food industry and minimize the risk of contamination of deli meat and associated food-contact surfaces.