Inactivation of Escherichia coli O157:H7 in Biofilm on Wooden Surfaces by Sequential Treatments of Aqueous Chlorine Dioxide and Drying

Introduction: Biofilm formation of Escherichia coli O157:H7 on the surface of food-cutting boards can be a source of cross-contamination of pathogens into foods.  Therefore, effective decontamination procedures to inactivate Escherichia coli O157:H7 on the surface of food-cutting boards should be developed.

Purpose: This study was done to evaluate the synergistic lethal effects of sequential treatments of aqueous chlorine dioxide (ClO₂) and drying against E. coli O157:H7 in biofilm on wooden surfaces.

Methods: Biofilms of E. coli O157:H7 on wooden coupons were produced in minimal salt broth at 22°C for 5 days.  Wooden coupons containing biofilms of E. coli O157:H7 were treated with 200 µg/ml of ClO₂ or sodium hypochlorite (NaOCl) solution for 10 min, thoroughly rinsed in sterile water, and subsequently dried with 43% relative humidity (RH) at 22°C for up to 12h.  The numbers of E. coli O157:H7 survived on wooden coupons after treatment of ClO₂or NaOCl solution and drying were measured.

Results: E. coli O157:H7 was able to form biofilms on wooden coupons (9.5 log CFU/coupon).  When the coupon containing the biofilm was treated with NaOCl solution, the population of E. coli O157:H7 on coupons decreased to 8.7 log CFU/coupon.  The subsequent drying caused 1.0 log CFU/coupon of additional reduction.  When coupons containing biofilm were treated with ClO₂ solution, the number of E. coli O157:H7 on coupons decreased to 7.6 log CFU/coupon.  The subsequent drying decreased the number of the pathogen on coupons by an additional > 7.0 log CFU/coupon.

Significance: Sequential treatment of aqueous ClO₂ and drying showed synergistic lethal effects in inactivating E. coli O157:H7 in biofilm on wooden surface.