Reduction of microbial populations and cross-contamination of Salmonella Typhimurium and the surrogate Enterococcus faecium on tomatoes during triple-wash using off-label concentrations of a combination of peroxyacetic acid and hydrogen peroxide

This study aims to determine the minimal concentrations of a 23% hydrogen peroxide and 5.3% peroxyacetic acid (H2O2-PAA) mixture required to prevent microbial cross-contamination of Salmonella and the potential surrogate Enterococcus faecium on tomatoes. Nalidixic acid-resistant (NaL) S. Typhimurium (5.15 log10MPN/g) or E. faecium (5.29 log10MPN/g) inoculated tomatoes were triple-washed for 45 s at each step using a water + antimicrobial + water (WAW) or water + water + antimicrobial (WWA) wash strategy with a solution of H2O2PAA at 0 (control) and off-label concentrations of 0.50 and 0.70%. A most probable number (MPN) method was used to analyze the microbial reductions and cross-contamination trasnferred cell counts. Significant reductions (P < 0.05) of Salmonella were only achieved when the off-label concentration of 0.7% H2O2-PAA was applied using the WWA strategy. When LS-Means were calculated, there were no significant differences (P > 0.05) in reductions of S. Typhimurium or E. faecium regardless of wash strategy. Cross-contamination of S. Typhimurium was prevented at 0.7% of H2O2-PAA using the WWA strategy, and E. faecium was prevented at and above 0.50% of H2O2-PAA, respectively, regardless of wash strategy. There were no differences (P > 0.05) of bacterial cell survival in triple-wash solutions between S. Typhimurium and E. faecium. Results suggested that E. faecium could be an acceptable surrogate for S. Typhimurium when validating antimicrobial washing systems on tomatoes. The off-label concentrations of H2O2-PAA that were tested resulted in non-detectable microbial cross-contamination. Off-label use of antimicrobials is not encouraged until future research determines the safety of these greater concentrations prior to their implementation in commercial settings.