Combination of low-energy X-ray and citric acid to inactivate Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes biofilms on stainless steel

This study evaluated the effectiveness of a combination of low-energy X-ray irradiation and citric acid (CA) treatment to control biofilms formed by Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on stainless steel surfaces. Combined treatment with 0.5 kGy X-ray and 0.1 % CA significantly decreased biofilm cell counts by 5.10, 4.31, and 3.96 log CFU/coupon for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively. The synergistic reduction observed with the combined treatment was at least 1.57, 1.55, and 1.35 log units for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, compared to the individual treatments. To elucidate the mechanisms underlying these synergistic anti-biofilm effects, quantitative analyses were performed on the key components of extracellular polymeric substances (EPS), including extracellular DNA (eDNA), proteins, polysaccharides, and ATP, as well as changes in biofilm-related gene expression. These results indicate that the combined X-ray–CA treatment synergistically reduced the polysaccharide content in EPS compared to the individual treatments. Moreover, the expression of genes associated with biofilm formation was downregulated. Overall, these findings highlight the potential of combined X-ray–CA treatment as an effective strategy for sanitizing food-contact surfaces and eliminating biofilms of foodborne pathogens in food-processing environments.