Listeria monocytogenes persistence and transfer to cantaloupes in the packing environment is affected by surface type and cleanliness

Investigation of the 2011 U.S. listeriosis outbreak associated with consumption of contaminated cantaloupes (Cucumis melo L) revealed that transfer of Listeria monocytogenes from equipment surfaces to melons in the packing facility was a potential route of contamination. The study presented here examined L. monocytogenes attachment and persistence on soiled materials and different types of equipment surfaces, and transfer to melons in a simulated-packing environment. Attachment involved the exposure of roller conveyors (polyvinyl chloride), conveyor belts (polyvinyl chloride, polyurethane, and nitrile rubber), and brush filaments (nylon and polyethylene) to ca. 7 log10 CFU/mL of a L. monocytogenes multi-strain inoculum for 10 and 60 min. L. monocytogenes showed similar (p > 0.05) attachment to all types of surfaces, and populations attached to surfaces following exposure for 10 min were not significantly different (p > 0.05) from that attached to surfaces after 60 min. Clean and soiled surfaces of nylon-brush filaments, conveyor belts, and foam pads were each inoculated with a L. monocytogenes multi-strain mixture (4.5 log10 CFU/mL) and subsequently stored at 25 °C, and L. monocytogenes populations on the surfaces were recovered for up to 15 days. L. monocytogenes populations on clean surfaces decreased from 4.5 log10 CFU/surface on day 0 to the detection limit by day 14; L. monocytogenes was still present on clean surfaces following enrichment on day 21. However, L. monocytogenes populations remained unchanged on soiled surfaces from day 0-14. Multivariate ANOVA revealed that soiled surfaces significantly (p < 0.05) promoted L. monocytogenes persistence compared to clean surfaces. Comparison of clean surfaces revealed that foam pads and brushes significantly (p < 0.05) promoted L. monocytogenes persistence compared to conveyor belt materials. Conveyor belts and foam pads were spot-inoculated (2.5 log10 CFU/surface), and 15 consecutive wet melons were manually rolled over each spot (n = 6 replicates), and melons were tested for the presence/absence of L. monocytogenes. Foam pads were found to contaminate significantly (p < 0.05) more melons than conveyor belts (polyvinyl chloride, polyurethane, and nitrile rubber). Soiled surfaces supported the survival of higher populations of L. monocytogenes, and surface type affected L. monocytogenes contamination transferred to specific melons.