Anti-Cariogenic Effects of Streptococcus salivarius G7 on Streptococcus mutans: An In Vitro Study

This study aimed to evaluate the anti-cariogenic potential of S. salivarius G7, a probiotic candidate. The antimicrobial activity of S. salivarius G7 against S. mutans was evaluated using a susceptibility assay, and its efficacy against S. mutans biofilm was assessed by confocal laser scanning microscopy (CLSM) and cultivation. The effect of S. salivarius G7 on the expression of glucosyltransferase (gtf) genes was examined by real-time reverse transcription-polymerase chain reaction (RT-PCR). Cariogenic biofilm models were also employed to investigate ecological effects. S. salivarius G7 inhibited the growth of S. mutans in a concentration-dependent manner and significantly reduced biofilm biomass and viable cell counts during biofilm development; however, it showed limited efficacy in disrupting mature biofilms. Gene expression analysis revealed a 20% – 35% reduction in the expression levels of gtf B, gtf C, and gtf D. In saliva-derived biofilms, treatment with S. salivarius G7 selectively decreased S. mutans abundance and enhanced S. salivarius colonization without altering total bacterial load. These findings demonstrate that S. salivarius G7 exerts anti-cariogenic effects by inhibiting growth, suppressing biofilm formation, downregulating glucan-related gene expression, and modulating microbial composition. The results support its potential as an oral probiotic for dental caries prevention.