1. Department of Food Science, Oregon State University, Corvallis, Oregon 97331
2. Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, Oregon 97331
3. Shinshu University School of Medicine, Matsumoto, Japan
4. National Animal Disease Center, Ames, Iowa 50010
5. Department of Microbiology, College of Science, Oregon State University, Corvallis, Oregon 97331