ABSTRACTN-acetylglucosamine (GlcNAc) and glucosamine (GlcN) enhance the competitiveness of the laboratory strain DL1 ofStreptococcus gordoniiagainst the caries pathogenStreptococcus mutans. Here we examine how amino sugars affect the interaction of five low-passage clinical isolates of abundant commensal streptococci withS. mutansutilizing a dual-species biofilm model. Compared to glucose, growth on GlcN or GlcNAc significantly reduced the viability ofS. mutansin co-cultures with most commensals, shifting the proportions of species. Consistent with these results, production of H2O2was increased in most commensals when growing on amino sugars, and inhibition ofS. mutansbyStreptococcus cristatus, Streptococcus oralis,orS. gordoniiwas enhanced by amino sugars on agar plates. All commensals exceptS. oralishad higher arginine deiminase activities when grown on GlcN, and in some cases GlcNAc. Inex vivobiofilms formed using pooled cell-containing saliva (CCS), the proportions ofS. mutanswere drastically diminished when GlcNAc was the primary carbohydrate. Increased production of H2O2could account in large part for the inhibitory effects of CCS biofilms. Surprisingly, amino sugars appeared to improve mutacin production byS. mutanson agar plates, suggesting that the commensals have mechanisms to actively subvert antagonism byS. mutansin co-cultures. Collectively, these findings demonstrate that amino sugars can enhance the beneficial properties of low-passage commensal oral streptococci and highlight their potential for moderating the cariogenicity of oral biofilms.SIGNIFICANCEDental caries is driven by dysbiosis of oral biofilms in which dominance by acid-producing and acid-tolerant bacteria results in loss of tooth mineral. Our previous work demonstrated the beneficial effects of amino sugars, GlcNAc and GlcN, in promoting the antagonistic properties of a health-associated oral bacterium,Streptococcus gordonii,in competition with the major caries pathogenStreptococcus mutans.Here we investigated 5 low-passage clinical isolates of the most common streptococcal species to establish how amino sugars may influence the ecology and virulence of oral biofilms. Using multiplein vitromodels, including a human saliva-derived microcosm biofilm, experiments showed significant enhancement by at least one amino sugar in the ability of most of these bacteria to suppress the caries pathogen. Therefore, our findings demonstrated the mechanism of action by which amino sugars may affect human oral biofilms to promote health.
Analysis of cariogenic potential of alternative milk beverages by in vitro Streptococcus mutans biofilm model and ex vivo caries model
