Phenotypic and genotypic characterization of Streptococcus mutans strains isolated from endodontic infections.

ABSTRACT Streptococcus mutans plays an important role in caries etiology and eventually in systemic infections. However, it is often found in infected root canals but the pathophysiological characteristics of strains residing in this site are largely unkonwn. Here, we characterized strains of S. mutans isolated from root canals of primary (PI) and secondary/persistent (SI) endodontic infections in relation to: serotype and genotype; presence of genes coding for collagen binding proteins (CBPs); collagen binding activity and biofilm formation capacity; ability to withstand environmental stresses; systemic virulence in Galleria mellonella; invasion of human coronary artery endothelial cells (HCAECs) and human dental pupal fibroblasts (HDPFs). Samples from 10 patients with PI and 10 patients with SI were collected and a total of 14 S. mutans isolates, belonging to three genotypes, were obtained. Of these, 13 were serotype c and 1 was serotype k. When compared to the reference strains, the clinical isolates were hypersensitive to hydrogen peroxide. Remarkably, all 14 strains harbored and expressed the CBP-encoding gene cbm showing increased binding to collagen, enhanced systemic virulence in G. mellonella and ability to invade HCAECs and HDPFs when compared to CBP-negative strains. Whole genome sequence analysis of PI and SI isolates revealed that these strains are phylogenetically related but genetically distinct from each other. Our findings highlight the importance CBPs in facilitating colonization and persistence of S. mutans in collagenous substrates such as root canals and their potential role in the pathogenesis of endodontic infections.