Abstract: The synergistic antibacterial effect and underlying mechanism of the antibacterial peptide brevilaterin combined with citric acid were studied against the food-borne pathogen Escherichia coli, with the aim to provide a theoretical basis for the application of this antibacterial peptide and citric acid in the control of E. coli. The effects of brevilaterin and citric acid on the membrane potential of E. coli were investigated by using DiSC3(5) fluorescence probe. The results showed that brevilaterin and citric acid could separately and synergistically dissipate the transmembrane potential of E. coli. Both of them could destroy membrane integrity as determined by propidium iodide/SYTO 9 probe marking combined with flow cytometry. Transmission electron microscopy (TEM) demonstrated that combination of brevilaterin with citric acid synergistically destroyed the ultrastructure of E. coli cells, specifically leading to cell deformation, plasmolysis and the leakage of cell contents. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that brevilaterin and citric acid had no significant effect on protein synthesis in E. coli. Agarose gel electrophoresis showed that brevilaterin and citric acid could separately and synergistically degrade the DNA of E. coli. Therefore, brevilaterin and citric acid can synergistically inhibit the growth of E. coli by disrupting the integrity of cell membrane and degrading bacterial DNA.

Key words: brevilaterin; citric acid; cell membrane integrity; bacterial DNA; synergistic antibacterial mechanism