Synergistic effects of silver ions and metformin against enterococcus faecalis under high-glucose conditions in vitro

Xuying Wu,Bing Fan,Wei Fan

doi:10.1186/s12866-021-02291-2

Abstract

BackgroundThis study aimed to evaluate the synergistic antibacterial activities of silver ions (Ag+) and metformin hydrochloride (Met) against Enterococcus faecalis (E. faecalis) under normal or high-glucose conditions.ResultsThe minimum inhibitory concentration, minimum bactericidal concentration, growth curves, and colony-forming units were used to evaluate the antibacterial effects of Ag+ and Met on planktonic E. faecalis in Brain Heart Infusion broth with or without additional glucose. The influences of Ag+ and Met on four weeks E. faecalis biofilm on human dentin slices was also tested. Cytotoxicity was tested on MC3T3-E1 osteoblastic cells using CCK-8 assays. The results indicated that E. faecalis showed higher resistance to drug treatment under high-glucose conditions. Ag+ (40 μg/mL) plus Met (3.2% or 6.4%) showed enhanced antibacterial activities against both planktonic E. faecalis and biofilm on dentin slices, with low cytotoxicity.ConclusionsMet enhanced the bactericidal effects of Ag+ against both planktonic and biofilm E. faecalis under normal or high-glucose conditions with low cytotoxicity. Further molecular studies are needed to be conducted to understand the mechanisms underlying the synergistic activity between Met and Ag+.

Highlights

This study aimed to evaluate the synergistic antibacterial activities of silver ions (Ag+) and metformin hydrochloride (Met) against Enterococcus faecalis (E. faecalis) under normal or high-glucose conditions
This study mainly focused on the synergistic inhibitory effect of Ag+ and Met on E. faecalis
The concentrations of metformin were selected based on the minimum inhibitory concentration (MIC) test of metformin and pilot studies

Summary

Introduction

This study aimed to evaluate the synergistic antibacterial activities of silver ions (Ag+) and metformin hydrochloride (Met) against Enterococcus faecalis (E. faecalis) under normal or high-glucose conditions. Bacteria remaining in the root canal system after initial treatment is often responsible for endodontic treatment failure and refractory apical periodontitis (AP) [1]. These bacteria can survive and proliferate in the treated root canal by feeding on tissue fluid rich in glycoprotein from the periapical area and induce or maintain inflammation around the periapical tissue [1]. Facultative anaerobic and gram-positive bacteria were reported to be the predominant flora in canals of treatment failure [2]. E. faecalis was reported to have a higher detection rate (33%) in the infected root canals of patients with diabetes than in healthy patients (19%) [9].

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