1. Public Health England, Porton Down, Salisbury SP4 0JG, UK
2. Respiratory and Vaccine Preventable Bacteria Reference Unit, Public Health England – Microbiology Reference Services, Colindale, 61 Colindale Avenue, London NW9 5EQ, UK
3. Department of Biology & Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK