1. Department of Biological Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan
2. Present address: GeneFrontier Co., 3-2-10 Nihonbashi-Kayabacho, Tokyo 103-0025, Japan
3. Second Department of Bacteriology, National Institute of Health, Kamiosaki, Shinagawa-ku, Tokyo 141, Japan
4. Department of Bacterial Pathogenesis and Infection Control, National Institute for Infectious Disease, 4-7-1 Gakuen, Musashimurayama-shi, Tokyo 208-0011, Japan