Abstract: In this study, the inhibitory effects of lactic acid (LA) and peracetic acid (PAA) on Escherichia coli O157:H7 biofilm formation were investigated, and the underlying mechanisms were explored with regard to the metabolic activity, the contents of extracellular polymeric substances (EPS), the microstructure of biofilm, and the expression of related functional genes. Results showed that the minimum inhibitory concentrations (MIC) of LA and PAA were 0.25% and 0.002 5%. The inhibitory effects of LA and PAA at sub-MIC on E. coli O157:H7 biofilm formation were weaker, as determined by the viable count method. Both organic acids at MIC showed significantly inhibitory effect (P < 0.05), and completely inhibited biofilm formation by E. coli O157:H7 at 2 MIC. After treatment with LA and PAA at MIC, the metabolic activity was reduced by 84.25% and 43.49%, and the contents of extracellular polymeric substances were also reduced significantly (P < 0.05). Both LA and PAA effectively inhibited the expression of E. coli O157:H7 biofilm adhesion-related genes (csgA and flhC), quorum sensing-related genes (luxS and sdiA), polysaccharide synthesis-related genes (csrA, adrB and adrA), and two-component regulatory system-related genes (phoQ, phoP, envZ and ompR). Therefore, LA and PAA can be used as potent disinfectants to reduce the risk of microbial contamination associated with food production and processing in the food industry.

Key words: Escherichia coli O157:H7; biofilm; lactic acid; peroxyacetic acid