<p>For surface analysis using scanning electron microscopy (SEM), infected native (A-C; patient 3) and prosthetic (D-F; patient 7) heart valve tissues were cut into small pieces and fixed. After pretreatment and exposure to osmium tetroxide, tissues were dehydrated and mounted on standard SEM stubs with carbon tape. The cured samples were finally sputter-coated with a platinum layer and evaluated with a scanning electron microscope. (A-C) SEM images of the surface of an infected native valve. (A) Overview. (B) Epithelial cell boundaries are discernable. Inset: note that few bacteria are attached to the smooth surface and that these seem to be often damaged (arrow). (C) At higher magnification scattered bacteria showing apparently intact morphology (arrow) can also be found. (D-F) Ultrastructure images of infected biological prosthetic valve. (D) Overview. (E) The surface is characterized by deep holes and cracks where microbes may be concealed; the surface appears rough. Inset: note that the few bacteria attached to the outside often seem to be damaged (arrow). (F) At higher magnification a number of apparently intact bacteria (arrows) showing different morphologies can be found; note the fibrous structure of the substrate, providing ideal adhesion sites.</p
