Buprenorphine enhances <i>Streptococcus mutans</i> virulence and biofilm formation

Background Buprenorphine is widely prescribed for opioid use disorder (OUD). In 2022, the U.S. FDA issued a safety warning on dental diseases associated with buprenorphine. While reports implicate increased caries risk, the microbial mechanisms remain unclear.Objective To evaluate whether buprenorphine directly modulates Streptococcus mutans (S. mutans) virulence traits relevant to cariogenesis.Design S. mutans UA159 were exposed to buprenorphine. Planktonic growth, acidogenicity, acid tolerance, aggregation, and carbohydrate utilization were assessed. Biofilm biomass and extracellular polymeric substance (EPS) production were quantified in hydroxyapatite disc–based monospecies and saliva-derived microcosm models. Biofilm architecture was evaluated using fluorescence in situ hybridization (FISH). The expression of competence- and biofilm-associated genes (comC, comX, gcrR, gtfB, and gtfC) was measured by RT-qPCR.Results Buprenorphine did not affect planktonic growth, acid production, or carbohydrate metabolism. However, it increased biofilm biomass and EPS production. FISH imaging revealed denser matrix-rich biofilms with closer spatial integration of S. mutans. Gene expression showed upregulation of comC, comX, gcrR, gtfB, and gtfC, indicating enhanced quorum sensing, stress adaptation, and matrix synthesis.Conclusions Buprenorphine promoted a biofilm-specific virulence program in S. mutans, fostering thicker, EPS-rich biofilms without altering planktonic physiology. These findings provide a mechanistic rationale for buprenorphine's association with caries risk.