1. Department of Microbiology, University of Oslo, Oslo, Norway
2. Present address: Lovisenberg Diaconal Hospital, Oslo, Norway.
3. Department of Microbiology, Oslo University Hospital, Oslo, Norway
4. Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Oxford Road, Manchester, UK
5. Present address: Department of Life Sciences and Health, Oslo and Akershus University College of Applied Sciences, Norway.