Enhanced in vitro antibacterial effect against Enterococcus faecalis by using both low-dose cetylpyridinium chloride and silver ions
Silei Lv, Wei Fan, Bing Fan
Abstract
Abstract Background Enterococcus faecalis ( E. faecalis ) is frequently isolated from root canals with failed root canal treatments. Due to the strong ability of E. faecalis to resist many often-used antimicrobials, coping with E. faecalis infections remains a challenge. The aim of this study was to investigate the synergistic antibacterial effect of low-dose cetylpyridinium chloride (CPC) and silver ions (Ag + ) against E. faecalis in vitro . Methods The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and the fractional inhibitory concentration index (FICI) were used to confirm the existence of the synergic antibacterial activity between low-dose CPC and Ag + . Colony-forming unit (CFU) counting, time-killing curve and dynamic growth curve were used to evaluate the antimicrobial effects of CPC and Ag + combinations against planktonic E. faecalis . Four weeks biofilms were treated with drug-contained gels to determine the antimicrobial effect on biofilm-resident E.faecalis , and the integrity of E.faecalis and its biofilms were observed by FE-SEM. CCK-8 assays was used to test the cytotoxicity of CPC and Ag + combinations on MC3T3-E1 cells. Results The results confirmed the synergistic antibacterial effect of low-dose CPC and Ag + against both planktonic and 4-week biofilm E. faecalis . After the addition of CPC, the sensitivity of both planktonic and biofilm-resident E. faecalis to Ag + improved, and the combination showed good biocompatibility on MC3T3-E1 cells. Conclusions Low-dose CPC enhanced the antibacterial ability of Ag + against both planktonic and biofilm E.faecalis with good biocompatibility. It may be developed into a novel and potent antibacterial agent against E.faecalis , with low toxicity for root canal disinfection or other related medical applications.