1. 1Foodborne Zoonoses Unit, Health Protection Agency, University of Bristol, Langford, Bristol BS40 5DU, UK
2. 2Oxoid Ltd., Basingstoke, Hampshire RG24 8PW, UK
3. 3Zoonotic Infections Group, School of Clinical Veterinary Science, Division of Veterinary Pathology Infection and Immunity, University of Bristol, Langford, Bristol BS40 5DU, UK