1Department of Microbiology, Gifu University School of Medicine, Tsukasa-machi 40, Gifu 500, Japan
2Institute for Chemical and Physical Research, Wako, Saitama 351, Japan
3Department of Bacteriology, Niigata University School of Medicine, Asahimachi-dori, Niigata 951, Japan
4Centers for Disease Control, Atlanta, Georgia 30333.
5Osaka Perinatal Medical Center and Research Institute, Izumi, Osaka 590-02, Japan