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 <i>E. coli</i> 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 <i>E. coli</i> 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 (<i>p <</i> 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 <i>Carnobacterium</i> and <i>Lactobacillus,</i> in combination with scrubbing, showed the greatest reduction of <i>E. coli</i> O157:H7. However, conditions such as mature or dry biofilms, lack of mechanical action, and treatment with hydrogen peroxide allowed <i>E. coli</i> O157:H7 survival, reflecting the structural resilience of biofilms and the pathogen's genetic tolerance to oxidative stress. Notably, <i>E. coli</i> 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: <i>Comamonas</i> and <i>Raoultella</i> were harder to control on TPU, and <i>Pseudomonas aeruginosa</i> was most resistant, especially in wet TPU biofilms at 10 °C.