1. Department of Fundamental Microbiology, Biology Building, University of Lausanne, CH-1015 Lausanne, Switzerland
2. Laboratory of Bacterial Pathogenesis, The Rockefeller University, 1230 New York Avenue, New York, New York 10021
3. Institute for Infectious Diseases, University of Bern, Friedbuehlstrasse 51, CH-3010 Bern, Switzerland