1. 1Public Health Laboratory Service, 61 Colindale Avenue, London NW9 5EQ, UK
2. 2Public Health Laboratory, Withington Hospital, Manchester M20 8LR, UK
3. 3Center of Marine Biotechnology, University of Maryland, Biotechnology Institute, 701 E. Pratt Street, Baltimore, Maryland 21202, USA
4. 4Department of Microbiology, University of Maryland, College Park, Maryland 20742, USA