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

## TL;DR

This study examines how different sanitizers affect E. coli O157:H7 and spoilage bacteria in biofilms under various conditions.

## Contribution

The study introduces a comprehensive evaluation of sanitizer efficacy in single- and multi-species biofilms under different environmental and mechanical conditions.

## Key findings

- BioDestroy® was the most effective sanitizer, achieving up to 7 log reductions on stainless steel.
- Scrubbing significantly reduced organic residues, lowering ATP readings from >14,000 to ~100–180.
- Mature or dry biofilms and hydrogen peroxide treatment allowed E. coli O157:H7 survival due to biofilm resilience and pathogen tolerance.

## Abstract

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.