Modulation of Lipoteichoic Acids and Exopolysaccharides Prevents Streptococcus mutans Biofilm Accumulation.

Dental caries is a diet-biofilm-dependent disease. Streptococcus mutans contributes to cariogenic biofilms by producing an extracellular matrix rich in exopolysaccharides and acids. The study aimed to determine the effect of topical treatments with compound 1771 (modulates lipoteichoic acid (LTA) metabolism) and myricetin (affects the synthesis of exopolysaccharides) on S. mutans biofilms. In vitro S. mutans UA159 biofilms were grown on saliva-coated hydroxyapatite discs, alternating 0.1% sucrose and 0.5% sucrose plus 1% starch. Twice-daily topical treatments were performed with both agents alone and combined with and without fluoride: compound 1771 (2.6 µg/mL), myricetin (500 µg/mL), 1771 + myricetin, fluoride (250 ppm), 1771 + fluoride, myricetin + fluoride, 1771 + myricetin + fluoride, and vehicle. Biofilms were evaluated via microbiological, biochemical, imaging, and gene expression methods. Compound 1771 alone yielded less viable counts, biomass, exopolysaccharides, and extracellular LTA. Moreover, the combination 1771 + myricetin + fluoride decreased three logs of bacterium counts, 60% biomass, >74% exopolysaccharides, and 20% LTA. The effect of treatments on extracellular DNA was not pronounced. The combination strategy affected the size of microcolonies and exopolysaccharides distribution and inhibited the expression of genes linked to insoluble exopolysaccharides synthesis. Therefore, compound 1771 prevented the accumulation of S. mutans biofilm; however, the effect was more pronounced when it was associated with fluoride and myricetin.

Extracellular DNA and lipoteichoic acids interact with exopolysaccharides in the extracellular matrix of Streptococcus mutans biofilms.

Streptococcus mutans-derived exopolysaccharides are virulence determinants in the matrix of biofilms that cause caries. Extracellular DNA (eDNA) and lipoteichoic acid (LTA) are found in cariogenic biofilms, but their functions are unclear. Therefore, strains of S. mutans carrying single deletions that would modulate matrix components were used: eDNA - ∆lytS and ∆lytT; LTA - ∆dltA and ∆dltD; and insoluble exopolysaccharide - ΔgtfB. Single-species (parental strain S. mutans UA159 or individual mutant strains) and mixed-species (UA159 or mutant strain, Actinomyces naeslundii and Streptococcus gordonii) biofilms were evaluated. Distinct amounts of matrix components were detected, depending on the inactivated gene. eDNA was found to be cooperative with exopolysaccharide in early phases, while LTA played a larger role in the later phases of biofilm development. The architecture of mutant strains biofilms was distinct (vs UA159), demonstrating that eDNA and LTA influence exopolysaccharide distribution and microcolony organization. Thus, eDNA and LTA may shape exopolysaccharide structure, affecting strategies for controlling pathogenic biofilms.

Inactivation of Streptococcus mutans genes lytST and dltAD impairs its pathogenicity in vivo.

Background: Streptococcus mutans orchestrates the development of a biofilm that causes dental caries in the presence of dietary sucrose, and, in the bloodstream, S. mutans can cause systemic infections. The development of a cariogenic biofilm is dependent on the formation of an extracellular matrix rich in exopolysaccharides, which contains extracellular DNA (eDNA) and lipoteichoic acids (LTAs). While the exopolysaccharides are virulence markers, the involvement of genes linked to eDNA and LTAs metabolism in the pathogenicity of S. mutans remains unclear. Objective and Design: In this study, a parental strain S. mutans UA159 and derivative strains carrying single gene deletions were used to investigate the role of eDNA (ΔlytS and ΔlytT), LTA (ΔdltA and ΔdltD), and insoluble exopolysaccharides (ΔgtfB) in virulence in a rodent model of dental caries (rats) and a systemic infection model (Galleria mellonella larvae). Results: Fewer carious lesions were observed on smooth and sulcal surfaces of enamel and dentin of the rats infected with ∆lytS, ∆dltD, and ΔgtfB (vs. the parental strain). Moreover, strains carrying gene deletions prevented the killing of larvae (vs. the parental strain). Conclusions: Altogether, these findings indicate that inactivation of lytST and dltAD impaired S. mutans cariogenicity and virulence in vivo.