1. Department of Microbiology and Immunology, School of Medicine and Dentistry, University of Rochester, Box 672, 601 Elmwood Avenue, Rochester, NY 14642, USA
2. Department of Microbiology, Section of Infectious Diseases, Boston University School of Medicine, Boston, MA 02118, USA
3. Department of Medicine, Section of Molecular Medicine, Boston University School of Medicine, Boston, MA 02118, USA