Polymethyl methacrylate microplastics affect oral microbiota diversity and Streptococcus mutans biofilm formation

Introduction Polymethyl methacrylate (PMMA)—a widely applied dental resin-based material—contributes to oral PMMA microplastics (PMMA-MPs) exposure through masticating. PMMA-MPs may facilitate pathogen adhesion, posing substantial risks to oral health. Dental caries represents the most prevalent chronic infectious oral disease, characterized by progressive lesions that may induce pain, tooth structure loss, and compromised masticatory efficiency. Streptococcus mutans have been widely identified as the primary etiological agents responsible for caries pathogenesis. This study aimed to investigate the effects of PMMA-MPs on oral microbiota closely associated with dental caries. Methods The impacts of PMMA-MPs were assessed using a standardized murine oral exposure model, followed by the quantification of PMMA-MPs-associated shifts in oral microbiota using high-throughput 16S rRNA gene sequencing. Compared with the control group, PMMA-MPs significantly altered the diversity of oral microbial communities in mice, with a notable increase in the relative abundance of Streptococcus . Based on the 16S sequencing results, S. mutans was selected for subsequent in vitro experiments. Results PMMA-MPs markedly enhanced the growth, biofilm formation, and virulence factor synthesis of S. mutans . Transcriptomic analysis revealed that PMMA-MPs may promote biofilm formation through pathways including ABC transporters, quorum sensing, and purine metabolism. Additionally, PMMA-MPs exposure enhanced bacterial antibiotic tolerance. Discussion Overall, our results revealed that PMMA-MPs can alter the composition of the oral microbial community, while enhancing both the virulence factors and antibiotic tolerance of S. mutans biofilms.