Abstract: The antibacterial activity and mechanism of juglone from walnut green husk against Escherichia coli were studied. E. coli was treated with juglone from walnut green husk in different concentrations. The minimum inhibitory concentration (MIC) of juglone was determined, and its effect on the growth curve, cell membrane relative conductivity, fluorescence emission spectrum, biofilm formation, cell viability, protein formation and genomic DNA and RNA synthesis of E. coli were investigated. The results showed that juglone had effective antibacterial activity against E. coli with an MIC value of 0.062 5 mg/mL. The relative conductivity of E. coli cell membrane increased after treatment with different concentrations of juglone, indicating that juglone destroyed the integrity of the cell membrane and increased the permeability. The results of fluorescence emission spectroscopy showed that juglone was able to interact with membrane proteins to change the membrane structure of E. coli cells. The results of crystal violet and resazurin staining showed that juglone could weaken the respiration of E. coli by inhibiting the formation of E. coli biofilms, thereby inhibiting its viability. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and E. coli genome synthesis analysis showed that juglone inhibited the expression of protein, DNA and RNA in E. coli. Through molecular docking, it was found that juglone can bind to the grooves of genomic DNA, thereby changing its secondary structure and morphology. In summary, juglone has a good inhibitory effect on E. coli, and can therefore be used as a natural antibacterial agent in the prevention and control of foodborne E. coli.

Key words: juglone; Escherichia coli; antibacterial activity; membrane protein; molecular docking