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Infect. Immun. doi:10.1128/IAI.00996-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Ability of Streptococcus agalactiae strains isolated from genital and neonatal specimens to bind to human fibrinogen, and fbs gene characteristics

Equipe d'Accueil 3854 - Institut Fédératif de Recherche 136 « Bactéries et risque maternofoetal » UFR Médecine, and Centre National de la Recherche Scientifique, Unité Mixte de Recherche 6542 « Physiologie des cellules cardiaques et vasculaires » UFR Sciences, Université François-Rabelais de Tours - France

^* To whom correspondence should be addressed. Email: rosenau{at}med.univ-tours.fr.

	Abstract

The ability of 111 S. agalactiae strains to bind to human fibrinogen was quantified. We correlated the percentages of bacteria that bound to immobilized fibrinogen with fibrinogen-binding (fbs) gene characteristics of strains and with clinical origin, serotypes and phylogenetic position of strains. Percentages varied from 0.4 to 29.9%. Fifty-five strains (49.5%) had the fbsB gene sensu stricto described by Gutekunst et al. allowing adhesion to human fibrinogen (Infect. Immun., 2004. 72:3495-3504) and all the other strains had a fgag variant gene. Ninety strains (81.1%) had a fbsA gene and 55 of them also had the fbsB gene. The other 21 strains (18.9%) had a truncated form of fbsA without the fbsB gene sensu stricto. The numbers of 48-nucleotide repeat sequences (rs) in the fbsA gene varied from 2 to 26. The population of strains with the highest ability to bind to human fibrinogen significantly more frequently had the fbsB gene sensu stricto and four to seven rs in the fbsA gene (P<0.05). However, the single strain that carried the highest number of rs (26 rs) in the fbsA gene showed high fibrinogen-binding activity (24.3%). Strains exhibiting significantly higher levels of binding to human fibrinogen belonged to a phylogenetic group of strains associated with neonatal meningitis, currently known as the ST-17 clone, that is mostly composed of serotype III strains. These findings indicate that S. agalactiae strains possess a wide variety of fbs gene content that markedly influences the ability of strains to bind to human fibrinogen. Variations in the configuration and the expression of the Fbs proteins may therefore partly explain the variability of virulence in S. agalactiae species.