Natural compounds for preventing dental caries by evaluating antibacterial and biofilm disrupting effects on Streptococcus mutans

Streptococcus mutans is a major contributor to dental caries, and its biofilm formation is associated with treatment challenges. Therefore, identifying medicinal plants and natural compounds with antibacterial and anti-biofilm activities is important for the development of new therapeutic approaches. This study aimed to investigate the antibacterial and anti-biofilm effects of honey, aqueous extracts of sumac and Miswak fruit, royal jelly, lactogum, and silver diamine fluoride (SDF) against S. mutans. The antibacterial effects of the compounds and extracts were evaluated using a well diffusion assay. The minimum inhibitory concentration (MIC) was determined by broth microdilution. Biofilm formation was quantified using the crystal violet assay, and metabolic activity was assessed by the MTT assay. Morphology of the biofilms was examined by scanning electron microscopy (SEM). Additionally, the expression of key genes involved in biofilm formation (gtfB, gtfC, and gtfD) was measured by RT-PCR. The findings indicated that the antibacterial effects of honey, Miswak aqueous extract, sumac fruit extract, and SDF were comparable to chlorhexidine. MICs were 512 mg/mL for honey, 512 mg/mL for sumac fruit extract, 512 mg/mL for royal jelly, and lactogum, with Miswak aqueous extract and SDF showing MICs of 256 mg/mL and 32 mg/mL, respectively. SDF, Miswak aqueous extract, and sumac fruit extract exhibited the strongest anti-biofilm effects, down-regulating gtfB, gtfC, and gtfD expression in S. mutans biofilms. Collectively, these results suggest that honey, Miswak and sumac aqueous extracts, and SDF have notable antibacterial activity against S. mutans and can inhibit biofilm formation through downregulation of gtfB, gtfC, and gtfD.