The fibronectin-binding protein homologue Fbp62 of Streptococcus anginosus is a potent virulence factor

Streptococcus anginosus appears to be able to adhere to cultured epithelial cells or fibronectin and this may be associated with bacterial pathogenicity. In the present study, the molecular characteristics and virulence of the fibronectin-binding protein (FBP), Fbp62, of S. anginosus were investigated in animal models to determine the role of the molecule in bacterial infection. fbp62 encodes a 549 amino acid residue with an apparent molecular mass of 62.8 kDa that lacks a membrane anchor motif and a leader peptide, suggesting that fbp62 codes for an atypical FBP. It has been observed that the S. anginosus Fbp62 is very similar to the FbpA of Streptococcus gordonii, PavA of Streptococcus pneumoniae, SmFnB of Streptococcus mutans and Fbp54 of Streptococcus pyogenes. Recombinant Fbp62 prepared from pGEX-4T-2 was found to bind to fibronectin in a dose-dependent manner and competitively inhibit the binding of S. anginosus to fibronectin. Furthermore, anti-Fbp62 antiserum abrogated the binding of S. anginosus to fibronectin. Adhesion of the isogenic mutant, Δfbp62, constructed from S. anginosus NCTC 10713 (wild-type, WT) by homologous recombination to HEp-2 cells and DOK cells was significantly weaker than that of S. anginosus WT. In addition, Δfbp62's lethality and ability to form abscesses were weaker in a mouse model of infection than in the WT strain. Taken together, these results suggest that Fbp62 is an important pathogenic factor of S. anginosus.