AUTHOR=Yu Haiyue , Ganas Petra , Schwendicke Falk 

TITLE=Environment-Specific Probiotic Supernatants Modify the Metabolic Activity and Survival of Streptococcus mutans in vitro

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01447

DOI=10.3389/fmicb.2020.01447

ISSN=1664-302X

ABSTRACT=<p>A range of studies showed probiotics like <italic>Streptococcus oligofermentans</italic> and <italic>Limosilactobacillus reuteri</italic> to inhibit the cariogenic activity and survival of <italic>Streptococcus mutans</italic>, possibly via the production of substances like H<sub>2</sub>O<sub>2</sub>, reuterin, ammonia and organic acids. We aimed to assess the environment-specific mechanisms underlying this inhibition. We cultured <italic>L. reuteri</italic> and <italic>S. oligofermentans</italic> 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) <italic>in vitro</italic>. Culture supernatants were obtained and metabolite concentrations (reuterin, ammonia, H<sub>2</sub>O<sub>2</sub>, lactate) measured. <italic>S. mutans</italic> 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 <italic>S. mutans</italic> was measured and its survival (as colony-forming-units/mL) assessed. <italic>L. reuteri</italic> environment-specifically produced reuterin, H<sub>2</sub>O<sub>2</sub>, ammonia and lactate, as did <italic>S. oligofermentans</italic>. When cultured in <italic>S. oligofermentans</italic> supernatants, lactate production by <italic>S. mutans</italic> was significantly reduced (<italic>p</italic> &lt; 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, <italic>p</italic> &lt; 0.001). A similar reduction in lactate production was found when <italic>S. mutans</italic> was cultured in <italic>L. reuteri</italic> supernatants (<italic>p</italic> &lt; 0.05) for all groups except MM+Lac+Glu. Survival of <italic>S. mutans</italic> cultured in <italic>S. oligofermentans</italic> supernatants in MM+Lac+Glu and MM+all was significantly reduced by 0.6-log<sub>10</sub> and 0.5-log<sub>10</sub>, respectively. Treatment with the supernatant of <italic>L. reuteri</italic> resulted in a reduction in the viability of <italic>S. mutans</italic> in MM+Gly+Glu and MM+all by 6.1-log<sub>10</sub> and 7.1-log<sub>10</sub>, respectively. Probiotic effects on the metabolic activity and survival of <italic>S. mutans</italic> were environment-specific through different pathways.</p>