1. Department of Biochemistry and Biomedical Sciences, Department of Chemistry and Chemical Biology, M. G. DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario L8N 3Z5, Canada.
2. Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198, USA.
3. Department of Microbiology and Immunology, and Centre for Human Immunology, University of Western Ontario, London, Ontario N6A 5C1, Canada.