Effect of graphene oxide-silver nanocomposites on Streptococcus mutans proliferation and biofilm formation

Abstract

Objective To investigate the effect of graphene oxide-silver nanocomposites (GO/Ag) on the proliferation and biofilm formation of Streptococcus mutans (S.mutans) . Methods Microdilution method was used to determine the minimum inhibitory concentration (MIC) of graphene oxide (GO) , silver-nanoparticles (AgNPs) , and GO/Ag nanocomposites against the S.mutans. For comparison of antibacterial efficiency of GO, AgNPs and GO/Ag, a colony-forming units counting method was applied. The biomass and the metabolic activities of biofilms with incubation of 24 h were tested by Crystal violet biofilm assay and XTT assay. Confocal laser scanning microscopy (CLSM) was performed to observe and calculate the percentage of live bacteria of S.mutans biofilm. The data were analyzed by One-Way ANOVA and LSD-t test. Results The MIC of GO/Ag nanocomposites against S.mutans was found to be 0.16 mg/mL. The bacteriostatic rate of 0.64 mg/mL GO/Ag was (82.90 ± 4.87) % and had significantly difference with the control group (t= 30.804, P<0.001) . In the GO and AgNPs groups, no apparent decrease of S.mutans could be observed, even after raising the concentration up to 2.56 mg/mL. In the 0.16 mg/mL GO/Ag group, reduction rate of biofilm biomass and metabolic activity were (25.12 ± 0.01) % and (38.90 ± 3.42) %, the percentage of live bacteria was (42.76 ± 19.48) %. All of these had significant difference with the blank control group (reduction rate of biofilm biomass: t= 7.274, P<0.001; reduction rate of metabolic activity: t= 7.765, P<0.001; percentage of live bacteria: t= 10.412, P<0.001) . Conclusions Comparing with AgNPs and GO, GO/Ag nanocomposites exhibited enhanced inhibition effect on the proliferation and biofilm formation of S.mutans. Key words: Streptococcus mutans; Nanocomposites, silver; Oxides, graphene; Anti-bacterial property