1. Hokkaido Institute of Public Health; Sapporo Hokkaido 060 Japan
2. Faculty of Bioindustry; Tokyo University of Agriculture; Abashiri Hokkaido 099-24 Japan
3. Faculty of Medicine; Okayama University; Okayama Okayama 700 Japan
4. Department of Microbiology; Sapporo Medical College; Sapporo Hokkaido 060 Japan