1. Danish Veterinary Institute, Bülowsvej 27, DK-1790 Copenhagen V, Denmark
2. University of Bern, Veterinary Bacteriology, Langgassstrasse 122, CH-3012 Bern, Switzerland
3. Department of Veterinary Microbiology, The Royal Veterinary and Agricultural University, Stigbøjlen 4, DK-1870 Frederiksberg C, Denmark
4. Institute for Medical Microbiology and Hygiene, Philipps-University, Pilgrimstein 2, D-35037 Marburg, Germany