1. Microbiology and Virology Unit, School of Medicine, University of Manchester, Oxford Road, Manchester M13 9PL, UK
2. Teagasc Food Research Centre, Alimentary Pharmabiotic Centre, Moorepark, Fermoy, Cork, Ireland
3. Department of Microbiology and Immunology, University of Otago, P.O. Box 56, Dunedin, Otago, New Zealand