1. Department of Microbiology; Nippon Dental University School of Dentistry at Tokyo; Chiyoda-ku Tokyo 102-8159 Japan
2. Scientific Instrument Center; Toyama Medical and Pharmaceutical University; Toyama 930-0152 Japan
3. Department of Oral Microbiology; Kyusyu Dental College; Kitakyushu Fukuoka 803-8580 Japan