Synergistic Antibacterial Activity of Berberine in Combination with Amylmetacresol Against Enterococcus faecalis in vitro

Objective To study the antibacterial effect of berberine combined with amylmetacresol on Enterococcus faecalis. Methods Both dilution method and live bacteria CFU were used to determine the minimum inhibitory concentration (MIC) of berberine and amylmetacresol on E. faecalis. The killing effect of berberine and amylmetacresol on planktonic E. faecalis was detected by suspension quantitative germicidal test and live/dead bacteria staining. The effects of berberine and amylmetacresol on the structure of mature biofilm of E. faecalis was observed by scanning electron microscopy (SEM). The toxicity of berberine and amylmetacresol on human oral keratinocytes (HOK) was determined by CCK-8 cell proliferation and cytotoxicity assay and cytotoxicity LDH assay. Results The MIC of berberine was 512 μg/mL, and the MIC of amylmetacresol was 0.023 3%. 512 μg/mL berberine and 0.002 33% amylmetacresol had a weak killing effect on planktonic E. faecalis alone, while they showed a synergistic antibacterial effect in combination. Cell survival in the biofilm was only slightly changed by berberine and amylmetacresol. The structure of biofilm was obviously changed by berberine and amylmetacresol. 512 μg/mL berberine and 0.002 33% amylmetacresol alone or in combination showed the survival rate was much higher than the injury rate, suggesting berberine and amylmetacresol had a low cytotoxicity. Conclusion Berberine and amylmetacresol had synergism against E. faecalis, and the biological safety of the combination use was better.