1. Department of Bacteriology, Swedish Institute for Infectious Disease Control, SE-171 82 Solna, Sweden
2. Department of Genetics, Microbiology and Toxicology, Stockholm University, SE-106 91 Stockholm, Sweden
3. Department of Laboratory Medicine, Karolinska Institute, SE-141 86 Stockholm, Sweden
4. Medical Products Agency, SE-751 03 Uppsala, Sweden
5. Lawrence Berkeley National Laboratory, Division of Earth Sciences, 1 Cyclotron Rd, Berkeley, CA 94720, USA
6. Department of Microbiology, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden