1. Institut Pasteur; Unité de Pathogénie Bactérienne des Muqueuses; Paris; F-75015; France
2. Department of Cellular Microbiology; Max-Planck Institute; Charitéplatz 1; D-10 117; Berlin; Germany
3. Institut Pasteur; Plate-Forme de Microscopie Ultrastructurale; Paris; F-75015; France
4. School of Biomolecular and Biomedical Sciences; University College Dublin; Ireland