Inhibitory Effect of Allyl Isothiocyanate on Cariogenicity of Streptococcus mutans

Allyl isothiocyanate (AITC) is a naturally occurring, pungent compound abundant in cruciferous vegetables and functions as a repellent for various organisms. The antibacterial effect of AITC against various bacteria has been reported, but there are no reports on the effect on Streptococcus mutans, a major bacterium contributing to dental caries. In this study, we investigated the inhibitory effect and mechanism of AITC on the survival and growth of S. mutans. AITC showed an antibacterial effect in a time- and concentration-dependent manner. In addition, bacterial growth was delayed in the presence of AITC, and there were almost no bacteria in the presence of 0.1% AITC. In a biofilm assay, the amount of biofilm formation with 0.1% AITC was significantly decreased compared to the control. RNA sequencing analysis showed that the expression of 39 genes (27 up-regulation and 12 down-regulation) and 38 genes (24 up-regulation and 14 down-regulation) of S. mutans was changed during the survival and the growth, respectively, in the presence of AITC compared with the absence of AITC. Protein-protein interaction analysis revealed that AITC mainly interacted with genes of unknown function in S. mutans. These results suggest that AITC may inhibit cariogenicity of S. mutans through a novel mechanism.