Amino Sugars Modify Antagonistic Interactions between Commensal Oral Streptococci and Streptococcus mutans

Abstract

N-Acetylglucosamine (GlcNAc) and glucosamine (GlcN) enhance the competitiveness of the laboratory strain DL1 of Streptococcus gordonii against the caries pathogen Streptococcus mutans. Here, we examine how amino sugars affect the interaction of five low-passage-number clinical isolates of abundant commensal streptococci with S. mutans by utilizing a dual-species biofilm model. Compared to that for glucose, growth on GlcN or GlcNAc significantly reduced the viability of S. mutans in cocultures with most commensals, shifting the proportions of species. Consistent with these results, production of H 2 O 2 was increased in most commensals when growing on amino sugars, and inhibition of S. mutans by Streptococcus cristatus, Streptococcus oralis, or S. gordonii was enhanced by amino sugars on agar plates. All commensals except S. oralis had higher arginine deiminase activities when grown on GlcN and, in some cases, GlcNAc. In ex vivo biofilms formed using pooled cell-containing saliva (CCS), the proportions of S. mutans were drastically diminished when GlcNAc was the primary carbohydrate. Increased production of H 2 O 2 could account in large part for the inhibitory effects of CCS biofilms. Surprisingly, amino sugars appeared to improve mutacin production by S. mutans on agar plates, suggesting that the commensals have mechanisms to actively subvert antagonism by S. mutans in cocultures. Collectively, these findings demonstrate that amino sugars can enhance the beneficial properties of low-passage-number commensal oral streptococci and highlight their potential for moderating the cariogenicity of oral biofilms. IMPORTANCE Dental 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 pathogen Streptococcus mutans. Here, we investigated 5 low-passage-number clinical isolates of the most common streptococcal species to establish how amino sugars may influence the ecology and virulence of oral biofilms. Using multiple in vitro models, 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.

Spontaneously Arising Streptococcus mutans Variants with Reduced Susceptibility to Chlorhexidine Display Genetic Defects and Diminished Fitness

“…At this point, all strains were inoculated individually (n ϭ 3) in CDM supplemented with 20 mM glucose and 5 mM sucrose by using 1:1,000 dilutions, along with an aliquot of cell-containing saliva (CCS) that was diluted 1:50 in CDM immediately after thawing from Ϫ80°C storage. Saliva samples for the CCS were originally collected and pooled from four healthy adult volunteers, all nonsmokers that had not taken antibiotics for at least 3 months prior to collection, as described previously (IRB201500497 at the University of Florida) (55). Then, 0.35 ml of the coinoculated medium was loaded into an ibidi 15 -Slide 8-well glass-bottom slide and incubated at 37°C in a 5% CO 2 aerobic atmosphere for either 24 h or 48 h, while another 0.1 ml was used for serial dilution and plating on mitis salivarius-bacitracin (MSB) agar supplemented with 1% tellurite, 20% sucrose, and 0.2 U ml Ϫ1 bacitracin to select for S. mutans (42) to determine the initial CFU count.…”

Novel Probiotic Mechanisms of the Oral Bacterium Streptococcus sp. A12 as Explored with Functional Genomics

“…Thus, the study of unique characteristics of certain key species in complex bacterial populations can provide considerable insights into the competitive and cooperative strategies that are employed by health-associated biofilms to persist and survive in particular ecological niches. Other examples of strain-specific inhibitory activities of commensals against pathogens are emerging (27,51). Commensal oral streptococci, like A12, that can express high ADS activity under environmental conditions commonly occurring in oral biofilms, can directly inhibit growth of S. mutans by producing H 2 O 2 , and can disable bacteriocin production via interference with the CSP-ComDE pathway ( 22) may provide substantial protection to a human host against dental caries.…”

Microbial Interactions in Oral Communities Mediate Emergent Biofilm Properties

“…For example, S. mutans produces several mutacins with antimicrobial activity against many other streptococci (Merritt and Qi 2012). S. gordonii and S. sanguinis of the Mitis group streptococci produce hydrogen peroxide as a by-product of carbohydrate metabolism (Redanz et al 2018; Chen et al 2019). While some oral microbes possess catalase genes and therefore resistance to oxidative stress, streptococci do not, and strains of S. mutans display a range of susceptibility to H 2 O 2 (Redanz et al 2018).…”