1. Department of Microbiology1 and
2. Department of Periodontology and Endodontology,2Hiroshima University School of Dentistry, Hiroshima 734-8553, Japan, and
3. Unité Associée INRA de Microbiologie Moléculaire, Ecole Nationale Vétérinaire de Toulouse, 31076 Toulouse Cedex, France3