1. Department Clinical Research, University of Bern, Murtenstrasse 35, 3010 Berne, Switzerland
2. Department of Biology, Chemistry and Pharmacy, Free University of Berlin, Takustrasse 6, 14195 Berlin, Germany
3. Institute of Microbiology, Technical University Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany