1. Department of Medical Microbiology and Immunology, College of Medicine and Public Health,
2. Department of Periodontology, College of Dentistry, Ohio State University, 333 West Tenth Avenue, Columbus, OH 43210, USA.
3. Department of Microbiology, Immunology, and Parasitology, Louisiana State University Medical Center, 1901 Perdido Street, New Orleans, LA 70112, USA.