1. Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322
2. Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611
3. Integrated Microscopy and Microanalytical Facility, Emory University, Atlanta, Georgia 30322
4. Department of Molecular and Cellular Biology and AFMnet-NCE, College of Biological Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1