1. School of Microbiological, Immunological and Virological Sciences, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
2. Johann Wolfgang Goethe-Universitaet Frankfurt, Institut für Mikrobiologie, Marie-Curie-Str., 9 Geb. N250, 60439 Frankfurt am Main, Germany
3. Department of Biochemistry & Genetics, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne NE2 4HH, UK