gallolyticus may play an important role in the predominance of this subspecies in S. bovis complex endocarditis. The endothelial cell line EA.hy926 displays

highly differentiated characteristics of human vascular endothelial [51] whereas primary endothelial cells such as HUVECs presumably provide the most accurate cell type based reflection of the in vivo situation. However, we observed no difference in the adhesion and invasion characteristics of S. gallolyticus using these two cell lines. Consequently, the usage of endothelial cell PRN1371 purchase lines seems to be an equivalent experimental in vitro model, with the major advantage of easier handling compared to primary cells. Nonetheless, it has to be noted that cell monolayers of either cell lines or primary cells only provide a two-dimensional model, whereas the in vivo situation

in tissue is three-dimensional. The intact endothelium is usually resistant to colonization find more by streptococci [18]. In the present study, mechanical stress of endothelial monolayer does not increase the proportion of adherent or invasive bacteria. This data is an indication for active colonization of valve tissue by S. gallolyticus. However, the results have to be interpreted with caution. We cannot exclude the possibility that mechanical stretch does not significantly increase the degree of stress on the potentially damaged cell monolayer. In addition, monolayers probably do not exhibit a physically Mannose-binding protein-associated serine protease intact endothelium

since two-dimensional cultivation or contact-inhibition perhaps affected the endothelial cells. Therefore, further studies are warranted to figure out the degree of monolayer integrity and the dimension of cell damage before and after mechanical stretch. The data of our study demonstrates that there is no evidence for the correlation between adherence to or invasion of endothelial cells, the adherence of bacteria to ECM proteins and biofilm formation. Therefore several other factors have to be investigated to determine their role in the infection of endothelial cells by S. gallolyticus isolates. These factors might include the capsule structure [52], interaction with cell surface glycosaminoglycans [53], presence of fimbriae or production of toxins [15]. It has been shown that S. gallolyticus is capable to produce capsular material [15] and the amount of capsule produced most likely influence the capacity to adhere to the cells. Hence, analysis of further pathomechanisms beneath adhesion, invasion and biofilm formation characteristics as well as the identification of further putative virulence genes is crucial for a better understanding of the mechanisms of S. gallolyticus infection. Our future investigations will address the transcriptional analysis of known virulence factors, the identification and characterization of further putative virulence genes by sequencing the whole genome of S.