Effects of Micro- and Nanoplastics on Human Saliva– and Dental Plaque–Derived Biofilms

Introduction and Aims Micro- and nanoplastics (MNPs) are ubiquitous environmental pollutants and are associated with health risks. Here, we investigated the effects of polystyrene micro- and nanoplastics (PS-MNPs) of different particle sizes and concentrations on saliva- and dental plaque–derived biofilms. Methods Colony-forming units and live/dead microbial staining were used to assess microbial count and viability, respectively. The anthrone assay and polysaccharide/microbial staining were used to determine extracellular polysaccharide (EPS) content. Acid production was assessed by supernatant pH and lactic acid concentration measurement. Reverse transcription quantitative polymerase chain reaction was used to determine the expression levels of acid and base production-associated genes. 16S rRNA gene sequencing was performed to characterise the microbial community at the genus level. Results PS-MNPs exposure reduced microbial count and viability in both biofilm types, although the magnitude of inhibition varied among treatments. No significant changes in EPS production were observed following PS-MNP exposure. In saliva-derived biofilms, 60-nm PS-MNPs at 1 and 10 µg/mL and 5-µm PS-MNPs at 1 µg/mL significantly increased lactic acid production, whereas 20-µm PS-MNPs at 100 µg/mL significantly reduced lactic acid production. In dental plaque–derived biofilms, only 60-nm PS-MNPs at 10 µg/mL inhibited lactic acid production. The supernatant pH decreased only after exposure to 10 and 100 µg/mL PS-MNPs in saliva-derived biofilms. Alkali-producing genes were downregulated, whereas the acid-producing genes were upregulated following PS-MNP treatment. Furthermore, only 5-µm MNPs at 100 µg/mL significantly increased richness and α-diversity in dental plaque–derived biofilm, whereas β-diversity remained unchanged in both biofilm types. PS-MNP exposure reduced the relative abundance of Neisseria and increased that of Limosilactobacillus in saliva-derived biofilm, whereas Porphyromonas, Fusobacterium, Actinomyces , and Schaalia increased in dental plaque–derived biofilm. Conclusions The effects of PS-MNPs on oral biofilms are dependent on size, concentration, and biofilm type. Clinical Relevance PS-MNPs can affect oral biofilms; however, their association with oral diseases warrants further investigation.