1. Department of Veterinary Microbiology, The Royal Veterinary and Agricultural University, Bülowsvej 13, DK-1870 Frederiksberg C, Denmark
2. Institut für Medizinische Mikrobiologie, Klinikum der Philipps-Universtät, Pilgrimstein 2, D-35037 Marburg, Germany
3. National Institute of Public Health, Department of Bacteriology, PO Box 4404 Torshov, 0403 Oslo, Norway