1. SAC Veterinary Services, Drummondhill, Stratherrick Road, Inverness IV2 4JZ, UK
2. Laboratory of Healthcare Associated Infection, Centre for Infections, Health Protection Agency, London NW9 5HT, UK
3. Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019-0245, USA
4. Institute of Zoology, Regent's Park, London NW1 4RY, UK
5. School of Food Biosciences, University of Reading, Reading RG6 6AP, UK