Competition and Caries on Enamel of a Dual-Species Biofilm Model with Streptococcus mutans and Streptococcus sanguinis.

Imbalances within the dental biofilm trigger dental caries, currently considered a dysbiosis and the most prevalent noncommunicable disease. There is still a gap in knowledge about the dynamics of enamel colonization by bacteria from the dental biofilm in caries. The aim, therefore, was to test whether the sequence of enamel colonization by a typically commensal and a cariogenic species modifies biofilm's cariogenicity. Dual-species biofilms of and on saliva-coated enamel slabs were inoculated in different sequences: followed by (Sm-Ss), followed by (Ss-Sm), and inoculated at the same time (Sm=Ss), and the single-species controls followed by (Sm-Sm) and followed by (Ss-Ss). Biofilms were exposed to 10% sucrose 3 times per day for 5 days, and the slabs/biofilms were retrieved to assess demineralization, viable cells, biomass, proteins, polysaccharides, and HO production. Compared with Sm-Sm, primary inoculation with reduced demineralization ( < 0.05). Both Ss-Sm and Sm=Ss sequences showed reduction in biomass, protein, and polysaccharide content ( < 0.05). The highest viable count and HO production level and the lowest acidogenicity were observed when colonized enamel before ( < 0.05). Initial enamel adherence with commensal biofilms seems to induce more intense competition against more typically cariogenic species, reducing cariogenicity. The concept of caries as an ecological disease implies the understanding of the intricate relationships among the populating microorganisms. Under frequent sugar exposure, some bacteria from the dental biofilm develop pathogenic traits that lead to imbalances (dysbiosis). Depending on which microorganism colonizes the dental surface first, different competition strategies may be developed. Studying the interactions in the entire dental biofilm is not an easy task. In this study, therefore, we modeled the interplay among these microorganisms using a caries-inducing species () and a health-associated species (). Initial enamel adherence with seems to induce more intense competition against typically caries-inducing species. Besides continuous exposure with sugars, early colonization of the enamel by highly cariogenic species like appears to be needed to develop caries lesions as well. Promoting early colonization by health-associated bacteria such as could help to maintain oral health, delaying dysbiosis.