1. Department of Pathology, Bacteriology and Poultry Diseases, Faculty of Veterinary Medicine, University of Ghent, B-9820 Merelbeke,1
2. Department of Clinical Chemistry, Microbiology and Immunology, Faculty of Medicine, University of Ghent,2 and
3. Laboratorium voor Microbiologie, Faculteit Wetenschappen, Universiteit Gent,3 B-9000 Ghent, Belgium