The role of exopolysaccharides and extracellular DNA in Streptococcus sanguinis evasion to complement system

Abstract

S. sanguinis is a comensal bacterial species that initiates tooth colonization and inhibits the grow of pathogenic species of biofilms, but which may also be involved in infective endocarditis after accessing the bloodstream from oral sites. Recently, we observed that S. sanguinis strains are resistant to deposition of C3b of the complement, a major opsonin involved in bacterial opsonophagocytosis by neutrophils (PMN) of the bloodstream. Additionally, our preliminary data suggest that production of exopolysaccharides (EPS) and extracellular DNA (eDNA) by S. sanguinis influences on bacterial susceptibility to complement deposition. The aim of this study is to investigate the roles of EPS and eDNA in S. sanguinis evasion to complement system. To that purpose, strains isolated from the oral cavity will be compared to strains isolated from the bloodstream of patients with bacteremia regarding their production of EPS and eDNA. The effects of removal of EPS and eDNA from the bacterial surface (through prior treatment of the clinical strains with dextranase or DNase I, respectively) in deposition of C3b and CAM of the complement and on opsonophagocytosis by PMN will be determined. In addition, isogenic mutants of genes required for production of EPS (gtfP) and eDNA (spxB), and of a gene potentially involved in S. sanguinis capacity to bind to eDNA (iga) will be constructed, and the effects of gene inactivation on deposition of C3b and CAM assessed after treatment of mutant and parent strains with human serum. The mutant strains will be compared with the parental strain regarding their susceptibility to opsonophagocytosis and killing by PMN isolated from human blood. The results obtained in this project might provide information about the molecular mechanisms by which S. sanguinis evade the complement system, which is important for the development therapies for controlling bacteremia and systemic infections by these microorganisms. (AU)