1. 1Institute of Veterinary Pathology, University of Zurich, Winterthurerstrasse 268, Zurich 8057, Switzerland
2. 2Department of Microbial Pathogenesis, University of Maryland Baltimore, USA
3. 3Institute of Microbiology University of Lausanne, Switzerland
4. 4Department of Microbiology and Ecosystem Science Division of Microbial Ecology, University of Vienna, Austria