1. Department of Microbiology and Immunology; University of British Columbia; Vancouver BC Canada V6T 1Z3
2. Institute for Cell and Molecular Biosciences, The Centre for Bacterial Cell Biology; Newcastle University; Newcastle Upon Tyne NE2 4AX UK
3. Agricultural Research Service, U.S. Department of Agriculture; Produce Safety and Microbiology Research Unit; Albany CA 94710 USA