Abstract: This study was done to determine the antibacterial activity and minimum inhibitory concentration (MIC) of berberine from the fruit of Berberis poiretii by the filter paper disk diffusion method and the spread plate method. Also, the antibacterial mechanism was explored by measuring the growth curve, conductivity, nucleic acid content and cell membrane Na+/K+-ATPase activity as well as conducting polyacrylamide gel electrophoresis (PAGE) analysis. The results showed that berberine had a certain inhibitory effect on four common bacteria with MICs for Escherichia coli, Bacillus subtilis, Staphylococcus aureus and Salmonella were 2.40, 3.60, 3.30 and 3.95 mg/mL, respectively, indicating it to be more effective against Escherichia coli. Scanning electron microscopy (SEM) showed that berberine damaged the morphology of the cells and ruptured the cells, leading to the leakage of intracellular substances and consequently an increase in the nucleic acid content in the bacterial suspension and an increase in electrical conductivity. PAGE analysis indicated that berberine could inhibit protein synthesis. In addition, it could reduce the Na+/K+-ATPase activity of the cell membrane. Therefore, berberine inhibits the expression of bacterial proteins by destroying the cell membrane structure, leading to the death of the cells so that it can exert good antibacterial effect. In conclusion, it can be used as a natural preservative to inhibit the growth of spoilage bacteria in foods so as to prolong the shelf life.

Key words: Berberis poiretii fruit; berberine; antibacterial activity; antibacterial mechanism