Combination therapy; a novel strategy for effective eradication of Enterococcus faecalis in vitro

Background: this study aimed to evaluate the effect of the intracanal medicines including Calcium hydroxide (CH), Zinc oxide nanoparticles (nZnO), Pantoprazole (PP), and Chlorhexidine (CHX) on Enterococcus faecalis ( E.faecalis) in the individual and combinatorial form in in-vitro design in order to introduce an effective medicine for eradication of E.faecalis . Methods: : E. faecalis (ATCC 29212) was used for bacterial assays. The powder and gel forms of the tested compounds were used in the analysis. The antibacterial and antibiofilm activities of the medicines were evaluated by the minimum inhibitory concentration (MIC) determination using the broth microdilution method. The anti-biofilm effect of medicines were assessed by minimum biofilm inhibitory concentration (MBIC).The antibacterial and antibiofilm effects of antimicrobial agent combinations were detected using the checkerboard assay and determination of Fractional Inhibitory Concentration Index (FICI). Time-kill kinetics were done at zero, 2, 4, 6, 8 10, 12, and 24 h. Results: : Except the MIC of the NaOCl which was significantly lower than CH, there was no statistically significant difference between groups in MIC, and MBIC. Only the mixture of chlorhexidine and zinc oxide nanoparticles (CHX-nZnO) and the mixture of pantoprazole and zinc oxide nanoparticles (PP-nZnO) had synergic effect against planktonic and biofilm form of the E.faecalis . Except for CHX and nZnO in gel form, other medicines did not show significant anti-biofilm effects against E.faecalis . Furthermore, CHX-nZnO in the gel form showed stronger anti-biofilm effects. Conclusion: Combination therapy would lead to higher antibacterial and anti-biofilm effects against E.faecalis comparing to conventional intracanal medicaments. Among these medicines, CHX-nZnO showed promising results.