1. Department of Oral and Molecular Microbiology, Osaka University Graduate School of Dentistry, Suita-Osaka 565-0871
2. PRESTO, Japan Science and Technology Corporation, Kawaguchi, Saitama 332-0012
3. Department of Virology, Osaka Prefectural Institute of Public Health, Osaka 537-0025
4. Department of Microbiology, Osaka Medical College, Takatsuki-Osaka 569-8686, Japan