Characterization and pathogenicity of fibronectin binding protein FbpI of Streptococcus intermedius
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ORIGINAL PAPER
Characterization and pathogenicity of fibronectin binding protein FbpI of Streptococcus intermedius Yoshitoyo Kodama1 · Yu Shimoyama1 · Taichi Ishikawa1 · Shigenobu Kimura1 · Minoru Sasaki1 Received: 24 January 2020 / Revised: 30 April 2020 / Accepted: 25 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Streptococcus intermedius is a causative agent of brain or liver abscesses. S. intermedius produces intermedilysin that plays a pivotal role in pathogenicity. We identified other pathogenic factors and described a fibronectin binding protein (FBP) homolog of S. intermedius (FbpI) that mediated bacterial adhesion to epithelial cells and virulence for mice. The amino acid sequence of FbpI is similar to that of atypical FBPs, which do not possess a conventional secretion signal and an anchoring motif. A full-length recombinant FbpI (rFbpI) bound to immobilized fibronectin in a dose-dependent manner. The fibronectin binding activity of an N-terminal construct of rFbpI comprising the translation initiation methionine of the open reading frame to lysine 265 (rFbpI-N) bound immobilized fibronectin to a much lesser extent compared with rFbpI. A construct comprising the C-terminal domain (alanine 266 to methionine 549; rFbpI-C) bound immobilized fibronectin equivalently to rFbpI. Adherence of the isogenic mutant ΔfbpI to cultured epithelial cells and immobilized fibronectin was significantly lower than that of the wild-type strain. Abscess formation of ΔfbpI reduced in a mouse infection model compared with that in the wild-type. Thus, FbpI may play a role in bacterial adhesion to host cells and represent a critical pathogenic factor of S. intermedius. Keywords Streptococcus intermedius · Fibronectin binding protein · Adherence · Epithelial cells · Pathogenicity
Introduction Streptococcus intermedius, a member of the anginosus group of streptococci, is a common commensal organism found in the human oral cavity and gastrointestinal and urogenital tracts (Whiley and Beighton 1991). However, S. intermedius is associated with purulent infections, abscesses, and infectious endocarditis (Gossling 1988; Fisher and Russell 1993; Willcox 1995; Tran et al. 2008). The organisms secrete the human-specific cytolysin intermedilysin (ILY) that is highly homologous to the cholesterol-binding cytolysin Communicated by Erko Stackebrandt. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00203-020-01922-y) contains supplementary material, which is available to authorized users. * Minoru Sasaki msasaki@iwate‑med.ac.jp 1
Division of Molecular Microbiology, Department of Microbiology, Iwate Medical University, 1‑1‑1 Idaidori, Yahaba‑cho, Shiwa‑gun, Iwate 028‑3694, Japan
streptolysin O (SLO) from S. pyogenes, pneumolysin from S. pneumoniae, and listeriolysin O (LLO) from Listeria monocytogenes. These proteins are members of the cholesteroldependent cytolysin family (Nagamune et al. 1996). ILY, which damages host cells such as human hepatic cells,
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