1. Nihon University Graduate School of Dentistry at Matsudo, Pediatric Dentistry, Matsudo, Chiba 271-8587, Japan
2. Department of Pediatric Dentistry, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan
3. Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan
4. Department of Infectious Disease, Kyorin University School of Medicine, Mitaka, Tokyo 181-8611, Japan
5. Department of Bacteriology, National Institute of Infectious Diseases, Shinjuku, Tokyo 162-8640, Japan