From the earliest scientific investigations into details of bacterial ultra structures scientists depended on microscopic methods to visualize the tiny microbes and their interaction with host cells. Therefore, there has been an intimate correlation between highly advanced microscopic imaging inventions and preparation techniques for the description of bacterial host cell interactions. Light microscopy was a hallmark of microbiology and with the introduction of confocal microscopes and high resolution light microscopy to image fluorescence labeled structures light microscopy gained momentum in the last two decades for studying bacterial interactions with host cells. Nevertheless, light microscopy reaches its limitations and electron microscopy pushed the visualization of bacterial interactions with cells forward. Nowadays, the combination of the two electron microscope types transmission electron microscopes (TEMs) and field emission scanning electron microscopes (FESEM) allows for detection of bacterial surface structures and their interaction with, for example, host cell receptors or extracellular matrix proteins as biding partner to establish adhesion to the host cell. Especially, FESEM opened up a new world of direct visualization of bacterial-cell interactions. In addition, imaging of ultrathin sections with TEMs provides access for internal structural features and interaction partners or for localization of pathogenicity factors.
The talk will provide an overview over the last 25 years of electron microscopic streptoccoccal research in Braunschweig in the former GBF and the present Helmholtz Centre for Infection Research, HZI. Most of the examples will deal with S. pyogenes and the interaction with different host cells. Developing of methods to detect recombinant proteins on bacterial surfaces, "kinetic studies" of receptor clustering and how to visualize intracellular trafficking following the classical endocytic pathway with electron microscopy. In addition, some examples of studies with S. suis and S. pneumoniae will also be presented.