Abstract
A range of studies showed probiotics like Streptococcus oligofermentans and Limosilactobacillus reuteri to inhibit the cariogenic activity and survival of Streptococcus mutans, possibly via the production of substances like H2O2, reuterin, ammonia and organic acids. We aimed to assess the environment-specific mechanisms underlying this inhibition. We cultured L. reuteri and S. oligofermentans in various environments; minimal medium (MM), MM containing glucose (MM+Glu), glycerol (MM+Gly), lactic acid (MM+Lac), arginine (MM+Arg) and all four substances (MM+all) in vitro. Culture supernatants were obtained and metabolite concentrations (reuterin, ammonia, H2O2, lactate) measured. S. mutans was similarly cultivated in the above six different MM variation media, with glucose being additionally added to the MM+Gly, MM+Lac, and MM+Arg group, with (test groups) and without (control groups) the addition of the supernatants of the described probiotic cultures. Lactate production by S. mutans was measured and its survival (as colony-forming-units/mL) assessed. L. reuteri environment-specifically produced reuterin, H2O2, ammonia and lactate, as did S. oligofermentans. When cultured in S. oligofermentans supernatants, lactate production by S. mutans was significantly reduced (p < 0.01), especially in MM+Lac+Glu and MM+all, with no detectable lactate production at all (controls means ± SD: 4.46 ± 0.41 mM and 6.00 ± 0.29 mM, respectively, p < 0.001). A similar reduction in lactate production was found when S. mutans was cultured in L. reuteri supernatants (p < 0.05) for all groups except MM+Lac+Glu. Survival of S. mutans cultured in S. oligofermentans supernatants in MM+Lac+Glu and MM+all was significantly reduced by 0.6-log10 and 0.5-log10, respectively. Treatment with the supernatant of L. reuteri resulted in a reduction in the viability of S. mutans in MM+Gly+Glu and MM+all by 6.1-log10 and 7.1-log10, respectively. Probiotic effects on the metabolic activity and survival of S. mutans were environment-specific through different pathways.
Highlights
The human oral cavity harbors more than 700 microbial species, which constitute a dynamic microbial community (Aas et al, 2005)
The supernatants resulting from the cultivation of probiotics in different environments were used to assess their impact on S. mutans metabolic activity, measured via determining the lactate production, and survival, measured via the colonyforming-units/mL of S. mutans
Reuterin was detected in both MM+Gly and MM+all (Figure 2A), while ammonia was only detected in MM+Arg (Figure 2B)
Summary
The human oral cavity harbors more than 700 microbial species, which constitute a dynamic microbial community (Aas et al, 2005). The coexistence and competition between different species are central to the oral microbial homeostasis (Bao et al, 2015). A disturbance in this homeostasis, termed dysbiosis, is associated with dental diseases like dental caries or periodontitis (Exterkate et al, 2010). The dominance of acidogenic and aciduric species like Streptococcus mutans, triggered by the abundant intake of fermentable carbohydrates, is associated with a net mineral loss from dental hard tissues and the formation of a caries lesion (Marsh, 2006). Contemporary caries management aims to rebuild a healthy microbial equilibrium within the dental biofilm (Marsh, 2006; Bao et al, 2015). Probiotics have been tested both in vitro and in clinical studies for their anticaries effect, with mixed results (Jalasvuori et al, 2012; Gruner et al, 2016)
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