1. Department of Applied Chemistry and Microbiology1 and
2. Institut für Angewandte Mikrobiologie, Justus-Liebig Universität, D-35390 Giessen, Germany2; and
3. Animal Reproduction, Department of Clinical Sciences, Saarentaus,3FIN-00014 University of Helsinki, and
4. Department of Food Microbiology, National Veterinary and Food Research Institute (EELA), 00231 Helsinki,4 Finland;
5. Food Hygiene Laboratory, Central Public Health Laboratory, Public Health Laboratory Service, London NW9 5HT, United Kingdom5