Dental Polymethyl Methacrylate Microplastics Induce Biofilm Formation In Streptococcus Mutans

This study investigates the in vitro and in vivo effects of polymethyl methacrylate (PMMA)-derived micro/nano-plastics (MNPs)—generated through denture abrasion—on Streptococcus mutans (S. mutans) growth and biofilm formation, given their emerging role as pollutants capable of altering oral microbiota and posing health risks. The 4-week-old male C57BL/6 mice were given oral gavage of 20µm and 80nm PMMA-MNPs for consecutive 4 weeks. We analyzed the abundance dynamics of Streptococcus within the oral microbial community via 16S rRNA sequencing. In vitro experiments, S.mutans was exposed to varying concentrations of 20µm and 80nm PMMA-MNPs, and growth curve was measured. The effects of PMMA-MNPs on S.mutans biofilms were evaluated through crystal violet staining, scanning electron microscopy, and live/dead bacterial staining. Concurrently, changes in extracellular polysaccharides(EPS) and antibiotic resistance of S.mutans were measured. Exposure to PMMA-MNPs resulted in a significant increase in the relative abundance of Streptococcus within the oral microbiota of mice. In vitro co-culture experiments, we demonstrated that PMMA-MNPs markedly enhanced the growth, biofilm formation, and EPS synthesis of S.mutans. Additionally, we also found that exposure to PMMA-MNPs enhanced bacterial antibiotic resistance. Our study demonstrated that PMMA-MNPs promoted the proliferation and biofilm formation of S.mutans, while enhancing bacterial virulence and antibiotic resistance.