1. Department of Microbiology; Jichi Medical School; Tochigi 329-0498 Japan
2. Third Department of Internal Medicine; Hokkaido University School of Medicine; Sapporo Hokkaido 060-8638 Japan
3. Department of Bacteriology; Okayama University Medical School; Okayama Okayama 700-8558 Japan
4. Animal Experimentation Center; Sapporo Medical University School of Medicine; Sapporo Hokkaido 060-8556 Japan
5. Department of Hygiene; Health Sciences University of Hokkaido; Hokkaido 061-0293 Japan