Efficacy of chemical sanitizers against E. coli O157:H7 in single- and multi-species biofilms under wet and dry conditions

Effective sanitation of food-contact surfaces is essential for controlling E. coli O157:H7 in beef processing environments. This study evaluated how environmental conditions (temperature, humidity, and biofilm age), surface materials stainless steel (SS) and thermoplastic polyurethane (TPU), mechanical action, and sanitizer type influence the survival of E. coli O157:H7 and spoilage bacteria within single- and mixed-species biofilms. Biofilms were formed on TPU and SS coupons at 10 °C or 25 °C, stored under wet 60–90% relative humidity (RH) and dry (20–50% RH) conditions at 10 °C and 25 °C for up to 60 days, and then exposed to detergents, a group was scrubbed other was not, then exposed to sanitizers quaternary ammonium compounds (Quats), sodium hypochlorite (Shypo), sodium hydroxide (SHyd), hydrogen peroxide (Hyp), peroxyacetic acid (PeroA) or BioDestroy ® . Results showed that sanitizer efficacy was strongly influenced by the interaction of biofilm age, scrubbing, and sanitizer type ( p 0.01). Across treatments, biocides achieved greater reductions on SS (up to 7 log) than on TPU (up to 5.6 log). BioDestroy ® , specifically formulated to eradicate biofilms, was the most effective sanitizer. ATP bioluminescence testing revealed that scrubbing markedly reduced organic residues, lowering RLU values from 14,000 on non-scrubbed surfaces to ~100–180 on scrubbed surfaces. Mixed-species biofilms containing Carnobacterium and Lactobacillus, in combination with scrubbing, showed the greatest reduction of E. coli O157:H7. However, conditions such as mature or dry biofilms, lack of mechanical action, and treatment with hydrogen peroxide allowed E. coli O157:H7 survival, reflecting the structural resilience of biofilms and the pathogen’s genetic tolerance to oxidative stress. Notably, E. coli O157:H7 was not detected on TPU or SS after 60 days of storage under either wet or dry conditions. Spoilage bacteria varied in resilience: Comamonas and Raoultella were harder to control on TPU, and Pseudomonas aeruginosa was most resistant, especially in wet TPU biofilms at 10 °C.