Interactions between endocarditis-derived Streptococcus gallolyticus subsp. gallolyticus isolates and human endothelial cells

Tanja Vollmer,Dennis Hinse,Knut Kleesiek,Jens Dreier

doi:10.1186/1471-2180-10-78

Abstract

BackgroundStreptococcus gallolyticus subsp. gallolyticus is an important causative agent of infective endocarditis (IE) but the knowledge on virulence factors is limited and the pathogenesis of the infection is poorly understood. In the present study, we established an experimental in vitro IE cell culture model using EA.hy926 and HUVEC cells to investigate the adhesion and invasion characteristics of 23 Streptococcus gallolyticus subsp. gallolyticus strains from different origins (human IE-derived isolates, other human clinical isolates, animal isolates). Adhesion to eight components of the extracellular matrix (ECM) and the ability to form biofilms in vitro was examined in order to reveal features of S. gallolyticus subsp. gallolyticus endothelial infection. In addition, the strains were analyzed for the presence of the three virulence factors gtf, pilB, and fimB by PCR.ResultsThe adherence to and invasion characteristics of the examined S. gallolyticus subsp. gallolyticus strains to the endothelial cell line EA.hy926 differ significantly among themselves. In contrast, the usage of three different in vitro models (EA.hy926 cells, primary endothelial cells (HUVECs), mechanical stretched cells) revealed no differences regarding the adherence to and invasion characteristics of different strains. Adherence to the ECM proteins collagen I, II and IV revealed the highest values, followed by fibrinogen, tenascin and laminin. Moreover, a strong correlation was observed in binding to these proteins by the analyzed strains. All strains show the capability to adhere to polystyrole surfaces and form biofilms. We further confirmed the presence of the genes of two known virulence factors (fimB: all strains, gtf: 19 of 23 strains) and demonstrated the presence of the gene of one new putative virulence factor (pilB: 9 of 23 strains) by PCR.ConclusionOur study provides the first description of S. gallolyticus subsp. gallolyticus adhesion and invasion of human endothelial cells, revealing important initial information of strain variability, behaviour and characteristics of this as yet barely analyzed pathogen.

Highlights

Streptococcus gallolyticus subsp. gallolyticus is an important causative agent of infective endocarditis (IE) but the knowledge on virulence factors is limited and the pathogenesis of the infection is poorly understood
S. gallolyticus subsp. gallolyticus is a normal inhabitant of the human gastrointestinal tract and numerous reports, referring to S. bovis, demonstrated an association between IE and gastrointestinal neoplasia, which were in most cases colonic adenoma or carcinoma [7,8,9] as well as liver disease [10,11]
Pathogenesis and several virulence factors have been examined for viridans streptococci, yet the knowledge of similar mechanisms for S. gallolyticus subsp. gallolyticus is limited

Summary

Introduction

Streptococcus gallolyticus subsp. gallolyticus is an important causative agent of infective endocarditis (IE) but the knowledge on virulence factors is limited and the pathogenesis of the infection is poorly understood. Gallolyticus is an important causative agent of infective endocarditis (IE) but the knowledge on virulence factors is limited and the pathogenesis of the infection is poorly understood. Gallolyticus, formerly referred to as Streptococcus bovis biotype I, a member of group D streptococci, was estimated to be the causative agent in 24% of streptococcal endocarditis [2]. Pathogenesis and several virulence factors have been examined for viridans streptococci, yet the knowledge of similar mechanisms for S. gallolyticus subsp. Sillanpää et al observed a difference in adherence to distinct host extracellular matrix (ECM) proteins of endocarditis-derived S. gallolyticus subsp. Viridans streptococci have been shown to adhere to human endothelial cells in vitro [16,17] and numerous host cell factors and bacterial components have been identified as possible virulence factor candidates in other streptococci [18]. It has been shown that pilB contributes to adherence to endothelial cells in groupB streptococci and over-expression leads to increased virulence in rats [22,23]

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