Molecules Targeting EriC^F1 Increase Streptococcus mutans Fluoride Sensitivity

Dental caries, as one of the prevalent oral infectious diseases worldwide, constitutes a considerable disease burden. Fluoride has been widely used to prevent dental caries for decades. However, fluoride alone may not always be sufficient. The major cariogenic bacterial species, Streptococcus mutans, has not been effectively controlled by daily fluoride exposure, possibly because it has a detoxification mechanism. Studies have shown that most microorganisms have fluoride exporters dedicated to exporting fluoride ions (F^-). S. mutans possesses 2 homologous genes, eriC^F1 and eriC^F2, which encode fluoride exporters, but their function has not been fully clarified. In this work, we constructed the markerless gene deletion mutants, overexpression, and complemented strains of S. mutans UA159. Assessing fluoride sensitivity, intracellular F^- levels, and cell membrane permeability revealed that EriC^F1 was the major functional unit of the fluoride exporter in S. mutans. To further enhance the antibacterial efficiency of fluoride, we identified 3 diphenylurea derivatives that might target EriC^F1 by molecular docking, which significantly enhanced the antibacterial effect of sodium fluoride (NaF) by synergistically impeding fluoride efflux, as demonstrated by chequerboard broth microdilution assays. Moreover, these compounds combined with 1 mM NaF impaired the cariogenicity of S. mutans significantly in vivo and with good biocompatibility, especially compounds 9 and 15. Collectively, these findings suggest that fluoride exporters in S. mutans could serve as a potential target for caries prevention, and the diphenylurea derivatives identified for targeting EriC^F1 could be a valuable therapeutic approach when combined with fluoride, providing promising measures for dental caries prevention.