Brazilin Combined With Fluoride Inhibits S. Mutans Biofilm Formation

To investigate the effects of brazilin combined with fluoride on the formation and metabolism of Streptococcus mutans (S. mutans) biofilm, so as to provide a theoretical foundation for developing anti-caries drugs. The inhibitory effect of brazilin and sodium fluoride (NaF) on S. mutans was evaluated using a checkerboard microdilution assay to determine the fractional inhibitory concentration (FIC) index. Biofilm formation was quantified via crystal violet staining after co-culturing S. mutans with 1% sucrose. Bacterial activity within the biofilm was assessed using the MTT assay. Acid production was measured by tracking pH changes with a Mettler Toledo pH electrode. Extracellular polysaccharide (EPS) synthesis was visualized and quantified using confocal laser scanning microscopy (CLSM). The FIC index of brazilin combined with NaF against S. mutans was 0.5315, indicating an additive interaction. Compared to control group, the brazilin combined with NaF significantly suppressed biofilm formation (reduced by 53.1%, P < 0.0001) and decreased bacterial activity (by 69%, P < 0.0001). Additionally, the brazilin combined with NaF inhibited acid production (final pH: 5.97 vs. 4.24 in control) and reduced EPS synthesis (EPS volume decreased by 42%, P < 0.001). The application of brazilin combined with fluoride demonstrates potent inhibitory effects on S. mutans biofilm formation and metabolism, its potential as a novel strategy for dental caries prevention.