Intravital fluorescence microscopy:: A novel tool for the study of the interaction of Staphylococcus aureus with the microvascular endothelium in vivo

Background. The ability of Staphylococcus aureus to adhere to endothelial cells is a major prerequisite for the tissue-invasive stage of bacterial infection. Methods. To develop a model for the study of endothelial attachment and detachment kinetics of S. aureus within the host's microvasculature in vivo, we labeled inactivated staphylococci with fluorescein isothiocyanate and investigated their interaction with the vascular endothelium of arterioles, capillaries, and venules in the dorsal skin-fold chamber of untreated and tumor necrosis factor (TNF)-alpha-treated hamsters by use of intravital fluorescence microscopy. Results. During the first 20 min after injection, >99% of the bacteria were removed from the microvascular bloodstream. In parallel, single bacteria and bacterial clusters adhered to the endothelial lining of postcapillary venules and to nutritive capillaries. Bacterial adherence to the endothelium of arterioles was only rarely observed. TNF-alpha treatment significantly accelerated bacterial clearance and resulted in a significant increase of venular, but not arteriolar and capillary, bacterial adherence, indicating the venular endothelium to be the target structure for bacterial recruitment. Conclusion. The insights into host-pathogen interaction gained with this new in vivo model offer highly promising novel aspects of the understanding of infections caused by S. aureus.