N-acyl-homoserine lactonase–nanosilver composite modulates the bacterial community of an in vitro enriched biofilm model of early childhood caries

Abstract

Objectives This study investigated the effects of a nanocomposite comprising N-acyl -homoserine lactonase Est816 and silver nanoparticles (Ag-Est816) on the microbial community of an enriched in vitro biofilm model derived from supragingival plaque of children with early childhood caries (ECC). Materials and methods Supragingival plaque samples were collected from 30 children aged younger than 6 years (15 males and 15 females) diagnosed with ECC. These samples were cultured in vitro to form biofilms, which were then treated with or without the Ag-Est816 composite for two days. The composition of the biofilms was analyzed by 16S rRNA sequencing to assess changes in α - and β -diversity, taxonomic composition, and predicted microbial functions. Biofilm morphology and biomass were evaluated using scanning electron microscopy (SEM) and crystal violet assays. Results The Ag-Est816 composite significantly reduced microbial α -diversity, including species richness and phylogenetic diversity (Chao1, Observed species, Faith's PD, p < 0.05). It also significantly altered overall bacterial community composition, as demonstrated by principal coordinate analysis (PCoA) and paired permutational multivariate analysis of variance (PERMANOVA), although the effect size was modest ( R 2 = 0.0286, P = 0.002). At the genus level, the abundances of Actinomyces , Lactobacillus , and Moryella were markedly decreased, whereas Haemophilus and Granulicatella were enriched. LEfSe analysis revealed Actinomyces and Lactobacillus as characteristic taxa enriched in the Control group, while Enterococcus and Granulicatella were significantly enriched following treatment. Functional prediction revealed that Ag-Est816 influenced pathways related to carbohydrate metabolism, amino acid biosynthesis, nucleotide metabolism, and nucleotide sugar biosynthesis. SEM imaging and biomass quantification confirmed that the Ag-Est816 composite disrupted biofilm architecture and significantly reduced total biomass. Conclusion The Ag-Est816 composite suppressed several low-abundance cariogenic genera while reducing overall community richness, altered microbial metabolic functions, and compromised biofilm structural integrity. These findings indicated this non-invasive nanocomposite has potential as an adjunctive therapy for caries prevention in children.

The authors' abstract, as published at the source. Frontiers in Oral Health, 2026 · DOI ↗