Antimicrobial effect of Viola odorata extract with or without zinc oxide nanoparticles on Streptococcus mutans

Objective: This study aimed to evaluate the antimicrobial efficacy of Viola odorata extract, with or without the addition of zinc oxide nanoparticles (ZnO NPs), against Streptococcus mutans.Methods: Two series of V. odorata hydroalcoholic extracts were prepared at concentrations of 25, 50, 100, and 200 mg/ml. Five hundred ppm ZnO NPs were added to 500 ml of the V. odorata extracts in half of the samples. The antibacterial activity of the extracts was then tested using the agar well diffusion method against S. mutans, and the inhibition zones were determined. The control groups were 0.2% chlorhexidine and Salvadora persica mouthwashes. Statistical analysis was performed using an independent-sample t-test, one-way ANOVA, and Duncan's post-hoc test (α=0.05).Results: Adding ZnO NPs significantly improved the inhibition zone of V. odorata extract at all concentrations (P < 0.05). The largest inhibition zone was observed in the 0.2% chlorhexidine mouthwash, significantly greater than all other groups (P < 0.001). The inhibition diameter for S. persica mouthwash was significantly greater than that of all the V. odorata extracts (P < 0.001), except for the group containing 200 mg/ml extract with ZnO NPs (P > 0.05).Conclusions: Adding 500 ppm ZnO NPs enhanced the antibacterial activity of the V. odorata extract. The antibacterial effect of the 200 mg/ml V. odorata extract combined with ZnO NPs was comparable to that of S. persica mouthwash against S. mutans. Given the anti-inflammatory and antibacterial properties of the V. odorata extract, this formulated mouthwash shows potential for improving patients' oral health.