Synergistic mechanism of Ag-Zn in anti-bacterial activity against Enterococcus faecalis and its application against dentin infection.

BACKGROUND

Ag and Zn have already been used in combinations to obtain both enhanced antibacterial effect and low cytotoxicity. Despite this, it is still unclear how the Zn co-works with Ag in the synergistic antibacterial activity. The main purposes of this study were to investigate the co-work pattern and optimum ratio between Ag and Zn in their synergistic antibacterial activity against E. faecalis, the possible mechanisms behind this synergy and the primary application of optimum Ag-Zn co-work pattern against the E. faecalis biofilm on dentin. A serial of Ag-Zn atomic combination ratios were tested on both planktonic and biofilm-resident E. faecalis on dentin, their antibacterial efficiency was calculated and optimum ratio determined. And the cytotoxicity of various Ag-Zn atomic ratios was tested on MC3T3-E1 Cells. The role of Zn in Ag-Znco-work was evaluated using a Zn pretreatment study and membrane potential-permeability measurement.

RESULTS

The results showed that the synergistically promoted antibacterial effect of Ag-Zn combinations was Zn amount-dependent with the 1:9 and 1:12 Ag-Zn atomic ratios showing the most powerful ability against both planktonic and biofilm-resident E. faecalis. This co-work could likely be attributed to the depolarization of E. faecalis cell membrane by the addition of Zn. The cytotoxicity of the Ag-Zn atomic ratios of 1:9 and 1:12 was much lower than 2% chlorhexidine.

CONCLUSIONS

The Ag-Zn atomic ratios of 1:9 and 1:12 demonstrated similar strong ability against E. faecalis biofilm on dentin but much lower cytotoxicity than 2% chlorhexidine. New medications containing optimum Ag-Zn atomic ratios higher than 1:6, such as 1:9 or 1:12, could be developed against E. faecalis infection in root canals of teeth or any other parts of human body.