Efficacy of Chemical Sanitizers Against E. coli O157:H7 in Single-and Multi-Species Biofilms Under Wet and Dry Conditions

Kavitha Koti¹Anna Macdonald¹Argenis Rodas-Gonzalez¹Tim McAllister^1,2Claudia Narvaez-Bravo^1*

• ¹University of Manitoba, Winnipeg, Canada
• ²Agriculture and Agri-Food Canada Lethbridge Research and Development Centre, Lethbridge, Canada

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: This is a provisional file, not the final typeset article Comamonas and Raoultella were harder to control on TPU, and Pseudomonas aeruginosa was most resistant, especially in wet TPU biofilms at 10 °C.