1. Department of Veterinary Microbiology, Faculty of Agriculture, Iwate University, Morioka, Iwate 020-8550
2. Department of Bacteriology, Hirosaki University School of Medicine, Zaifu-cho, Hirosaki 036-8562
3. Department of Technical Support and Development, National Institute of Radiological Sciences, Inage-ku, Chiba-shi 263-8555, Japan