1. Department of Food Hygiene and Environmental Health, Faculty of Veterinary Medicine, P.O. Box 66; University of Helsinki; FI-00014 Helsinki Finland
2. Norwegian School of Veterinary Science; Dept. of Food Safety and Infection Biology; P.O. Box 8146 Dep. 0033 Oslo Norway
3. Haartman Institute, Department of Bacteriology and Immunology, P.O. Box 21; University of Helsinki; FI-00014 Helsinki Finland
4. National Food Administration; P.O. Box 622 SE-75126 Uppsala Sweden
5. Department of Animal Science, Inter-Department Program in Microbiology, 215F Meat Laboratory; Iowa State University; Ames IA 50011
6. National Food Institute, Technical University of Denmark; Mørkhøj Bygade 19 DK-2860 Søborg Denmark