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P3-92 Practices and Conditions which Promote Persistence of Listeria monocytogenes on Equipment Surfaces and Transfer to Cantaloupes in the Packing Environment

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Esmond Nyarko , University of Delaware , Newark , DE
Kalmia Kniel , University of Delaware , Newark , DE
Bin Zhou , U.S. Department of Agriculture–ARS , Beltsville , MD
Cheryl East , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Eric Handy , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Yaguang Luo , U.S. Department of Agriculture–ARS , Beltsville , MD
Patricia Millner , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Manan Sharma , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Introduction: Investigation of the 2011 United States listeriosis outbreak associated with contaminated cantaloupes revealed that transfer of Listeria monocytogenes (Lm) from equipment surfaces to melons in the packing facility was a potential route of contamination.

Purpose: This study examined Lm persistence on unclean materials and different types of surfaces and the transfer to cantaloupes in a simulated packing environment.

Methods: Clean and unclean (0.5 ml cantaloupe extract; dried 6 h) surfaces of nylon brush bristles (1 g), and 16 cm2 of conveyor belts (polyvinyl-chloride, polyurethane, and nitrile-rubber), and foam-pads (16 cm2) were prepared. Each surface was inoculated with a multistrain Lm cocktail (4.5 log CFU/ml), and subsequently stored at 25°C. Lm populations on surfaces were recovered for up to 15 days. A separate set of inoculated unclean surfaces received water (1 ml) 24 h prior to each enumeration event. Conveyor belt and foam pad materials were spot-inoculated (50 µl; 2.5 log CFU/surface) and 15 consecutive wet melons were manually rolled over each spot. Melons were tested for presence/absence of Lm.

Results: Lm populations decreased from 4.5 on day zero to 0, 2.3±0.5, and 3.1±0.2 log CFU/surface on clean conveyor belts, brush, and foam-pad materials, respectively, by day 10. Lm was still present on clean surfaces after 21 days. However, Lm populations remained unchanged (4.5 log CFU/surface) on unclean surfaces from days zero to 14. Multivariate ANOVA revealed that unclean surfaces significantly (P<0.05) promoted persistence of Lm compared to clean surfaces. Comparison of clean surfaces revealed that foam pad and brush significantly (P<0.05) promoted Lm persistence more than polyurethane, polyvinyl-chloride, and nitrile-rubber. An ANOVA of probability distributions of contaminated melons (n=90 melons per surface) revealed that foam pad contaminated significantly (P<0.05) more melons (78±5%) than polyvinyl-chloride (55±11%), which was approximately equivalent to polyurethane (47±9%) and nitrile-rubber (33±10%) belts. There was no correlation between the presence of Lm on melons and the order in which they were exposed to contaminated surfaces.

Significance: Unclean surfaces and materials that retain water promoted persistence and widespread contamination of melons.

Back to: Poster Session 3 – Low-water Activity Foods, Packaging, Produce, Microbial Food Spoilage, Antimicrobials, Laboratory and Detection Methods, Water
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