1. Department of Surgical Sciences; University of Cagliari; Via Porcell, 4 09100 Cagliari Italy
2. Cell and Molecular Microbiology Division; Institute of Microbiology; v.v.i.; Academy of Sciences of the Czech Republic; Vídeňská 1083 14220 Prague Czech Republic
3. Centre for Bacterial Cell Biology; Institute for Cell and Molecular Biosciences; Newcastle University; Richardson Road Newcastle upon Tyne NE2 4AX UK