Persistence and sanitizer tolerance of Listeria monocytogenes biofilms on nonmetal food-contact surfaces in dairy processing environments.

Listeria monocytogenes, a major foodborne pathogen linked to listeriosis outbreaks and dairy product recalls, can persist in dairy processing environments by forming biofilms, posing a persistent contamination risk. This study investigated the biofilm-forming ability of multi-strain L. monocytogenes on 5 nonmetal food-contact surfaces commonly used in dairy processing facilities: Buna-N, Viton, ethylene propylene diene monomer (EPDM), silicone rubber, and Teflon. The tolerance of established biofilms to commonly used sanitizers, peroxyacetic acid (PAA), quaternary ammonium compounds (QAC), and chlorine, was evaluated in relation to surface aging and the presence of organic matter. Biofilm density was significantly higher on Buna-N, EPDM, and silicone rubber surfaces than on Teflon. PAA was the most effective sanitizer, achieving reductions in 2-d-old biofilms ranging from 3.2 log cfu/coupon on EPDM to 3.8 log cfu/coupon on Buna-N, and in 7-d-old biofilms ranging from 2.7 log cfu/coupon on EPDM to 3.9 log cfu/coupon on Teflon following a 1 min treatment at 100 ppm. In contrast, the antibacterial efficacy of QAC and chlorine was significantly reduced on aged Buna-N, EPDM, and Teflon surfaces compared with new surfaces. Although the presence of milk residues did not significantly affect sanitizer efficacy against L. monocytogenes biofilms on new Buna-N, EPDM, and Teflon surfaces, QAC and chlorine were less effective on aged Teflon in the presence of milk residues. The findings suggest that nonmetal surface materials commonly used in dairy processing facilities can support L. monocytogenes persistence and influence sanitizer tolerance, underscoring the importance of effective cleaning practices, routine surface maintenance, and informed selection of food-contact surface materials to mitigate contamination risks in dairy-processing environments.