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

The 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.Our 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.Viridans streptococci are the most important pathogens responsible for native valve infective endocarditis (IE) in non-drug-addicted patients [1]. However, Streptococcus gallolyticus subsp. 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]. S. gallolyticus subsp. gallolyticus belongs to the S. bovis-complex including different species frequently isolated from humans and animals (S. bovis, S. gallolyticus, S. infantarius, S. equinus, S. alactolyticus). The taxonomic classification of this group of streptococci was often revised. However, at the beginning of this decade, Schlegel et al. proposed the reclassification of S. bovis biot