1. Rhodes College Biology Department, 2000 North Parkway, Memphis, TN 38112, USA
2. Microbiology and University of Washington, Seattle, WA 98195, USA
3. Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Victoria 3000, Australia
4. Laboratory Medicine, University of Washington, Seattle, WA 98195, USA