1. Department of Bacteriology; The Kitasato Institute; Minato-ku Tokyo 108-8642 Japan
2. Department of Preventive and Community Dentistry; The Nippon Dental University, School of Dentistry at Tokyo; Chiyoda-ku Tokyo 102-8159 Japan
3. Department of Oral Microbiology; Kanagawa Dental College; Yokosuka Kanagawa 238-8580 Japan
4. Center of Microbiology and Virology; Polish Academy of Sciences; Lodowa 106 93-232 Lodz Poland