Antibacterial Efficacy of Walnut Green Husk (WGH) Extract with Zinc Oxide Nanoparticles on Streptococcus Mutans

Background: Chemical agents, such as Chlorhexidine are used as one of dental plaque control strategy. Researchers are looking for a natural and economic substitute with same antibacterial efficacy and less complications. The aim of this study was to evaluate the antimicrobial efficacy of the Khorasan Razavi walnut green husk extract with and without adding ZnO nanoparticles (nZnO) on  (S. mutans). Methods: In this in vitro study, antimicrobial effect of the Hydro-ethanolic extract of WGH, was evaluated. Broth Dilution and Agar diffusion methods were used with 90 tubes containing different dilutions of WGH extract (100 to 0.006 mg/ml). ZnO nanoparticles (nZnO) were added to 45 tubes. Streptococcus mutans was exposed to 15 different serial concentrations of study extracts, from 100 mg/ml to 0.006 mg/ml. Minimum inhibitory concentration (MIC) of the study extracts were determined and zone of inhibition diameter was compared to positive controls (chlorhexidine 0.2%, nZnO), and negative control (sterile distilled water). The differences between the mean diameters, were analyzed by independent sample T- teS. Results: Minimum inhibitory concentration (MIC) of study extract was found to be 50 mg/mL, with adding nZnO, MIC was reduced to 3.12 mg/mL. Mean diameter of inhibition zone at 3.12 mg/ml with and without adding ZnO nanoparticles were 17.67±0.57 mm and 8±0.001 mm, respectively, (p-value 0.001). Conclusions: Adding nZnO could be enhanced antimicrobial efficacy of the WGH extract against S. mutants, while it was still less effective than chlorhexidine.