1. Department of Oral Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3, Gengo, Morioka, Obu, Aichi 474-8522, Japan
2. Laboratory of Oral Molecular Microbiology, Department of Oral Pathobiological Science, Hokkaido University Graduate School of Dental Medicine, Sapporo 060-8586, Japan
3. Department of Infectious Diseases, St. Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, Tennessee 38105