[S6-3] Characterization and pathogenicity of fibronectin binding protein of anginosus group of streptococci
Anginosus group of streptococci (AGS) are causative agent of infective endocarditis and abscesses of the brain or liver. Although bacterial adhesion to host tissues is a critical step in infection, the mechanisms of AGS have not been clarified. We have identified fibronectin-binding protein (FBP) in AGS that could mediate adhesion to host cells. The FBP of Streptococcus anginosus and S. intermedius does not contain the transmembrane motifs or a leader peptide, suggesting this it is an atypical FBP. The antigenic similarity of FBP was recognized among oral streptococci with anti-S. intermedius FBP antiserum. The recombinant FBP bound to immobilized fibronectin in a dose-dependent manner. In addition, the adherence of the isogenic mutant (Δfbp) to immobilized fibronectin and epithelial cells was reduced compared with that of the wild-type. Western blotting and immunofluorescence analysis revealed that FBP localized to the bacterial cell surface. Furthermore, the binding domain of FBP molecule was revealed in the C-terminal using recombinant N-terminal (amino acid residues 1–265) and C-terminal (amino acid residues 266–549) constructs. The Δfbp was less pathogenic compared to the wild-type, in the mouse infection model. Taken together, FBP of AGS play a role of adherence to host cells and may be an important virulence factor in these bacterial infections.