Synergistic bactericidal effect of hot water and citric acid against pathogens in biofilm formed on food contact surface

Abstract

This study investigated the antimicrobial effect of hot water with citric acid against Escherichia coli O157:H7 in biofilm formed on stainless steel (SS). The hot water with citric acid of 50, 60, or 70°C exhibited synergistic bactericidal effect on the pathogen biofilm. At this time, it was shown that sub-lethally injured cells should be considered when applying this technology because it generated sub-lethally injured cells. Meanwhile, in this study, the mechanisms of the synergistic bactericidal effects of hot water with citric acid were identified through several approaches. In terms of biofilm matrix, hot water removes polysaccharide, a major component of the extracellular polymeric substances (EPS), to increase the contact of the surface cells and citric acid, resulting in a synergistic bactericidal effect. In terms of the cell itself, increased permeability of citric acid through cell membranes destructed by hot water promotes the inactivity of superoxide dismutase (SOD) in E. coli O157:H7, resulting in a synergistic generation of reactive oxygen species (ROS), and thus these ROS lead synergistic cell death by activating synergistic incidence of lipid peroxidation, which induces synergistic destruction of cell membrane. Therefore, it is interpreted that when hot water with citric acid is applied to the E. coli O157:H7 biofilm on SS, the synergy effects on the biofilm matrix and cell itself have a complex interaction with each other, thus causing a dramatic synergistic bactericidal effect. Based on these results, I conducted the experiments on pipe to evaluate applicability of this combined treatment in the food industry.