Intraspecies interactions ofStreptococcus mutansimpact biofilm architecture and virulence determinants in childhood dental caries

Abstract

Early childhood dental caries (ECC) is the most common chronic disease among children with a heavy disease burden among low socioeconomic populations.Streptococcus mutansis most frequently associated with initiation of ECC. Many studies report children with multipleS. mutansstrains (i.e., genotypes) having greater odds of developing ECC, studies investigating intraspecies interactions in dental caries are lacking. In this study, the impact of intraspecies interactions on cariogenic and fitness traits of clinicalS. mutansisolates are investigated usingin-vitroandin-vivoapproaches.Initially clinicalS. mutansisolates of 10 children from a longitudinal epidemiological study were evaluated.S. mutansstrains (G09 and G18, most prevalent) isolated from one child were used for subsequent analysis. Association analysis was used to determine if presence of multipleS. mutansgenotypes within the first-year of colonization was associated with caries. Biofilm analysis was performed for single and mixed cultures to assess cariogenic traits, including biofilm biomass, intra-polysaccharide, pH, and glucan. Confocal Laser Scanning Microscopy (CLSM) and time-lapse imaging were used to evaluate spatial and temporal biofilm dynamics, respectively. ADrosophilamodel was used to assess colonizationin-vivo.Mean biofilm pH was significantly lower in co-cultured biofilms as compared with monoculture biofilms. Doubling ofS. mutans in-vitrobiofilms was observed by CLSM andin-vivocolonization inDrosophilafor co-culturedS. mutans. Individual strains occupied specific domains in co-culture and G09 contributed most to increased co-culture biofilm thickness and colonization inDrosophila. Biofilm formation and acid production displayed distinct signatures in time-lapsed experiments.IMPORTANCEThis study sheds light on the complex dynamics of a key contributor to early childhood dental caries (ECC) by exploring intraspecies interactions of differentS. mutansstrains and their impact on cariogenic traits. Utilizing clinical isolates from children with ECC, the research highlights significant differences in biofilm architecture and acid production in mixed versus single genotype cultures. The findings reveal that co-culturedS. mutansstrains exhibit increased cell density and acidity, with individual strains occupying distinct domains. These insights, enhanced by use of time-lapsed Confocal Laser Scanning Microscopy and a Drosophila model, offer a deeper understanding of ECC pathogenesis and potential avenues for targeted interventions.