Dental caries is a costly and prevalent disease characterized by the demineralization of the tooth's enamel. Disease outcome is influenced by host factors, dietary intake, cariogenic bacteria, and other microbes. The cariogenic bacterial species Streptococcus mutans metabolizes sucrose to initiate biofilm formation on the tooth surface and consequently produces lactic acid to degrade the tooth's enamel. Persistence of S. mutans biofilms in the oral cavity can lead to tooth decay. To date, no anticaries therapies that specifically target S. mutans biofilms but do not disturb the overall oral microbiome are available. We screened a library of 2-aminoimidazole antibiofilm compounds with a biofilm dispersion assay and identified a small molecule that specifically targets S. mutans biofilms. At 5 µM, the small molecule annotated 3F1 dispersed 50% of the established S. mutans biofilm but did not disperse biofilms formed by the commensal species Streptococcus sanguinis or Streptococcus gordonii. 3F1 dispersed S. mutans biofilms independently of biofilm-related factors such as antigen I/II and glucosyltransferases. 3F1 treatment effectively prevented dental caries by controlling S. mutans in a rat caries model without perturbing the oral microbiota. Our study demonstrates that selective targeting of S. mutans biofilms by 3F1 was able to effectively reduce dental caries in vivo without affecting the overall oral microbiota shaped by the intake of dietary sugars, suggesting that the pathogenic biofilm-specific treatment is a viable strategy for disease prevention.

SUMMARY The oral cavity is a dynamic environment characterized by hundreds of bacterial species, saliva, and an influx of nutrients and metal ions such as copper. While there is a physiologic level of copper in the saliva, the oral cavity is often challenged with an influx of copper ions. At high concentrations copper is toxic and must therefore be strictly regulated by pathogens in order to persist and cause disease. The cariogenic pathogen Streptococcus mutans manages excess copper using the copYAZ operon that encodes a negative DNA-binding repressor (CopY), the P1-ATPase copper exporter (CopA), and the copper chaperone (CopZ). These hypothetical roles of the copYAZ operon in regulation and copper transport to receptors led us to investigate their contribution to S. mutans virulent properties. Mutants defective in the copper chaperone CopZ, but not CopY or CopA, were impaired in biofilm formation and competitiveness against commensal streptococci. Characterization of the CopZ mutant biofilm revealed a decreased secretion of glucosyltransferases and reduced expression of mutacin genes. These data suggest that the function of copZ on biofilm and competitiveness is independent of copper resistance and CopZ is a global regulator for biofilm and other virulence factors. Further characterization of CopZ may lead to the identification of new biofilm pathways.