Preliminary Study On The Inhibitory Effect And Mechanism Of Gallic Acid On The Biofilm Formation Of Staphylococcus Aureus And Shigella Flexneri

Staphylococcus aureus and Shigella flexneri are common pathogenic bacteria in food industry,in addition to the direct cause of food contamination,there is another important feature is that they can form biofilm on food and the food processing equipment.Biofilm is difficult to eliminate and it can lead to food contamination through a variety of ways,resulting in a great danger in food safety.The aim of this study was to investigate the inhibitory effect of gallic acid on biofilm formation of Staphylococcus aureus and Shigella flexneri,and primary to explore the mechanism of inhibiting biofilm formation,to provide a new method for the control of food contamination caused by bacterial biofilm,and lay the foundation for further study on the mechanism of gallic acid inhibiting bacterial biofilm formation.In this study,we investigated the inhibitory effect of gallic acid on biofilm formation of two pathogens,namely Staphylococcus aureus(S.aureus)and Shigella flexneri(Sh.flexneri).Principal results are as follows:1.The MIC and MBC of gallic acid against S.aureus and.flexneri in suspension was 2 mg/mL and 8 mg/mL,respectively.The MIC and MBC of gallic acid against S.aureus in biofilm were 4 mg/mL and 32 mg/mL,respectively.The results showed that gallic acid had effective antibacterial and bactericidal activity on S.aureus and Sh.flexneri.2.The results showed that 0.25 mg/mL of gallic acid can inhibit biofilm formation of S.aureus and Sh.flexneri,the inhibition rate of biofilm was 68.3%and 78.98%after exposure to 2 mg/mL of gallic acid,respectively.Gallic acid was proved to have effective anti-biofilm activities against S.aureus and Sh.flexneri,it is mainly because the inhibitionof the polysaccharide formation.The degree of inhibition of biofilm formation was higher with increasing gallic acid concentrations as a dose-dependent relationship.3.The results showed that gallic acid could penetrate the biofilm to kill the S.aureus and Sh.flexneriin biofilm.4.The mechanism that gallic acid inhibit the S.aureus biofilm formation may be related to the expression of the ica operon gene family.The results showed that icaR was significantly activated and icaA and icaD were downregulated in a dose-dependent manner with increasing concentrations of gallic acid,but the expression of icaB and icaC was not significantly affected.5.The inhibition mechanism of gallic acid on biofilm formation of Sh.flexneri may be achieved by inhibiting the expression of mdoH gene and its protein product OpgH protein,and inhibiting the GTF enzyme activities of Sh.flexneri,thereby inhibiting the synthesis of polysaccharides of Sh.flexneri and biofilm formation was inhibited.