1. Institute of Veterinary Pathology, Department of Pathobiology, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 268, CH-8057 Zurich, Switzerland
2. Centre for Microbiology and Environmental Systems Science, Department of Microbiology and Ecosystem Science, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria
3. Institute of Microbiology, University of Lausanne, Bugnon 48, CH-1011 Lausanne, Switzerland