1. Division of Microbiology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
2. Eiken Chemical Co. Ltd, 143 Nogi Nogimachi, Shimotsuga-gun, Tochigi 329-0114, Japan
3. Saitama Institute of Public Health, Saitama 338-0824, Japan