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

Abstract

Imbalances within the dental biofilm trigger dental caries, currently considered a dysbiosis and the most prevalent non-communicable 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 Streptococcus mutans (Sm) and Streptococcus sanguinis (Ss) on saliva-coated enamel slabs were inoculated in different sequences: Sm followed by Ss (Sm-Ss), Ss followed by Sm (Ss-Sm), Sm and Ss inoculated at the same time (Sm=Ss) and the single-species controls Sm followed by Sm (Sm-Sm) and Ss followed by Ss (Ss-Ss). Biofilms were exposed to 10% sucrose, 3x/day for 5 days and the slabs/biofilms were retrieved to assess demineralization, viable cells, biomass, proteins, polysaccharides and H2O2 production. When compared with Sm-Sm, primary inoculation with Ss reduced demineralization (p<0.05). Both Ss-Sm and Sm=Ss sequences showed reduction in biomass, protein and polysaccharide content (p<0.05). The highest S. sanguinis viable cells and H2O2 production and the lowest acidogenicity were observed when Ss colonized enamel before Sm (p<0.05). Initial enamel adherence with commensal biofilms seems to induce more intense competition against more typically cariogenic species, reducing cariogenicity. Importance The concept of caries as an ecological disease implies the understanding of the intricate relationships among the populating microorganisms. Under frequent sugars 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 article, therefore, we modeled the interplay among these microorganisms using a caries-inducing (S. mutans) and a health-associated species (S. sanguinis). Initial enamel adherence with S. sanguinis 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 S. mutans, appears to be needed to develop caries lesions, as well. Promoting early colonization by health-associated bacteria, such as S. sanguinis, could help to maintain oral health, delaying dysbiosis.

Predominance of non-Streptococcus mutans bacteria in dental biofilm and its relation to caries progression

“…It also agrees with Richards et al ( Richards et al, 2017 ) who reported that R. aeria was more common in caries free than caries active adolescents from Sweden and Romania. Our study showed greater abundance of S. sanguinis in high caries individuals and this disagrees with Hurley et al ( Hurley et al, 2019 ); Díaz-Garrido et al, ( Díaz-Garrido et al, 2020 ) and Richards et al ( Richards et al, 2017 ) who both reported greater abundance of S. sanguinis in caries free than caries active children. Meric and colleagues reported similar frequencies of S. mutans, and S. sanguinis among caries and caries free groups of subjects ( Meriç et al, 2020 ).…”

E-Cigarette Aerosol Exposure Favors the Growth and Colonization of Oral Streptococcus mutans Compared to Commensal Streptococci

“…S1) and support the idea that the opportunistic growth of S. mutans is not due to a growth kinetic advantage, since the commensals grew when cultured alone in the same time frame. Overall, these data suggest that S. mutans can outcompete both S. sanguinis and S. gordonii , consistent with previous research on the competition between S. sanguinis and S. mutans in the oral cavity ( 25 – 28 ).…”

Testing of candidate probiotics to prevent dental caries induced by Streptococcus mutans in a mouse model

“…Dental colonization of S. mutans was unaffected by the subsequent administration of either strain of BCC23 after prior establishment of S. mutans under cariogenic conditions. In a dual-species biofilm model with S. sanguinis SK36 and S. mutans UA159 in which each species was seeded on enamel slabs, establishment of S. mutans prior to introducing S. sanguinis, when compared to first establishing S. sanguinis, resulted in biofilms having greater levels of the following characteristics: medium acidity, loss of enamel surface microhardness, total biomass, total protein and recovery of viable S. mutans, but with a lower recovery of S. sanguinis and a lower concentration of H 2 O 2 in the medium (Diaz-Garrido et al, 2020). Thus, once S. mutans establishes a dental biofilm with a dense glucanrich, acidic and oxygen-depleted environment, it may be highly effective at fending off competitors.…”