Impact of surface type and sanitizer use on reduction of Listeria monocytogenes biofilms subjected to varying nutrient availability

The ability of Listeria monocytogenes to attach to surfaces and form a biofilm while surviving in cold environments increases the risk of cross-contamination in the food processing environment (FPE). This study aims to determine which food contact surface (FCS) materials favor L. monocytogenes biofilm formation and survival under a nutrient-promoting and nutrient-limiting condition. The antimicrobial efficacy of three sanitizers (5% lactic acid, 200 ppm chlorine, 200 ppm quaternary ammonium compound) against biofilms formed under the two nutrient environments was also studied. A five-strain cocktail of L. monocytogenes grown in tryptic soy broth (TSB) was used to develop biofilms on four different FCS coupons (1 × 1 cm): acetal, nitrile, rubber, and stainless steel. Under the nutrient-promoting condition, coupons were subjected to a 72-h incubation period consisting of TSB refreshment every 24 h followed by sanitizer treatment. Nutrient-limiting coupons were subjected to the treatments after an additional 14-day storage period at 4.4°C with no nutrients following the initial 3-day incubation period. Results demonstrated biofilm-associated cell populations exceeded 6.75 log CFU/cm 2 on all surface types under the nutrient-promoting condition. The nutrient-limiting condition resulted in reduced microbial populations on all surface types of 6.21-6.48 log CFU/cm 2 . While sanitizer efficacy was dependent on surface type, all sanitizers achieved significant reductions ( P <0.05) in comparison to the control under both conditions. Lactic acid consistently resulted in a greater reduction ( P <0.05) throughout both conditions. This study affirms the ability of L. monocytogenes to adhere to and form a biofilm on various food contact surfaces utilized in the FPE, to survive in a nutrient-depleted environment, and may suggest that sanitizer efficacy against biofilms is dependent on the surface type used as a substrate.