Combined Effects of Sanitizers and UV-C Light on Listeria monocytogenes Biofilm Growth and Survivability on Produce-Harvesting Materials Used in the Tree Fruit Production Industry

Listeria monocytogenes is an aggressive biofilm former that can establish and persist in food processing environments. Commonly associated with ready-to-eat and dairy products, this pathogenic bacterium has recently been increasingly linked to fresh produce outbreaks. Equipment used during harvesting and handling of produce can provide a niche environment for biofilm growth and persistence. Based on a survey conducted among stakeholders in the tree fruit production industry, three favored materials for storing and harvesting produce were identified: nylon, wood, and plastic. The purpose of this study was to investigate the application of the generally recognized as safe sanitizers lactic acid, thymol, and silver citric acid (SDC) and UV-C light alone or in combination for 2 or 5 min on different food-contact surfaces used during tree fruit harvesting and storing. Multistrain L. monocytogenes biofilms were grown in a Centers for Disease Control and Prevention biofilm reactor for 96 h on wood, nylon, and polycarbonate coupons at 20 ± 2°C. After each treatment, coupons were neutralized and the remaining cells were enumerated. Results showed that the most effective treatment was the simultaneous use of UV-C light and SDC (4-log reduction) and that the least effective treatment was UV-C light alone (P < 0.05). The type of material was found to play a significant role in the efficacy of the sanitizers (P < 0.05). This study demonstrates the ability of L. monocytogenes to grow and form biofilms on different surfaces and contributes to an understanding of the response of this food safety threat against antimicrobial intervention strategies.