Streptococcus Rubneri Attenuates Cariogenic Virulence Of Streptococcus Mutans

To investigate whether Streptococcus rubneri, enriched in caries-free children, attenuates the cariogenicity of Streptococcus mutans through phenotypic interference and gene-level suppression. S. rubneri was isolated from oral samples of 3–6-year-old children via culturomics and confirmed by 16S rRNA sequencing. In vitro co-culture assays were conducted to evaluate bacterial growth (OD600), acidogenicity (pH monitoring), biofilm formation (Crystal Violet assay and SEM), and extracellular polysaccharide (EPS) synthesis (confocal microscopy, anthrone-sulfuric acid assay). qPCR assessed the expression of virulence genes (gtfA-D, ftf, gbpB, brpA). In vivo effects were validated in a rat model of caries via Keyes scoring and micro-CT imaging. S. rubneri significantly inhibited S. mutans growth and acid production, suppressed biofilm biomass and EPS formation, and downregulated genes involved in glucan synthesis and matrix regulation. In rats, co-inoculation with S. rubneri reduced caries severity and enamel demineralization. S. rubneri exerts multilevel suppression of S. mutans pathogenicity through phenotypic inhibition and virulence gene downregulation, supporting its potential as a probiotic candidate for caries prevention.