Control of pathogens in biofilms on the surface of stainless steel by levulinic acid plus sodium dodecyl sulfate

Abstract

The efficacy of levulinic acid (LVA) plus sodium dodecyl sulfate (SDS) to remove or inactivate Listeria monocytogenes, Salmonella Typhimurium, and Shiga toxin-producing Escherichia coli (STEC) in biofilms on the surface of stainless steel coupons was evaluated. Five- or six-strain mixtures (ca. 9.0logCFU/ml) of the three pathogens were separately inoculated on stainless steel coupons. After incubation at 21°C for 72h, the coupons were treated for 10min by different concentrations of LVA plus SDS (0.5% LVA+0.05% SDS, 1% LVA+0.1% SDS, and 3% LVA+2% SDS) and other commonly used sanitizers, including a commercial quaternary ammonium-based sanitizer (150ppm), lactic acid (3%), sodium hypochlorite (100ppm), and hydrogen peroxide (2%). The pathogens grew in the biofilms to ca. 8.6 to 9.3logCFU/coupon after 72h of incubation. The combined activity of LVA with SDS was bactericidal in biofilms for cells of the three pathogens evaluated, with the highest concentrations (3% LVA+2% SDS) providing the greatest log reduction. Microscopic images indicated that the cells were detached from the biofilm matrix and the integrity of cell envelopes were decreased after the treatment of LVA plus SDS. This study is conducive to better understanding the antimicrobial behavior of LVA plus SDS to the foodborne pathogens within biofilms.