Streptococcus sanguinis (SS) is a pioneer species of teeth, which inhibits pathogenic species of dental biofilms, but is frequently involved in infective endocarditis through mechanisms as yet unknown. Our recent results indicate that SS has low susceptibility to deposition of C3b of the complement system, a major opsonin involved in blood clearance by neutrophils (PMN) or other blood cells. The aim of this project is to investigate the molecular mechanisms involved in SS resistance to complement-mediated opsonization. To this end, SS strains isolated from dental plaque and from the bloodstream will be characterized regarding their binding to serum proteins which activate (SAP, C1q, ficolina L) or inhibit (C4BP, Fator H, FHL1 e C1-INH) the complement. Genes potentially involved in these phenotypes will be then investigated, including covRSs (encodes a transcriptional regulator of virulence CovR) and genes likely regulated by CovRSs, which encode C3 proteases (pepOSs and cppASs). Transcript levels of covRSs, pepOSs and cppASs will be compared between the isolates by RT-qPCR. Isogenic mutants of these genes will be obtained in strain SK36, and characterized regarding their binding to C3b, to soluble proteins involved in activation and inhibition of the complement and to fibronectin. Mutant strains with altered phenotypes will be then compared to parent strain regarding their susceptibilities to opsonophagocytosis by PMN from human blood. The results of this project may help to elucidate mechanisms which modulate SS susceptibility to complement-mediated immunity, an important topic for the development of therapies to control systemic infections by this species.
News published in Agência FAPESP Newsletter about the scholarship: