TABLE 1.

Bacterial strains used in this study

Strain	Source or description
Nissle 1917	Obtained from Paul S. Cohen, Department of Cell and Molecular Biology, University of Rhode Island, Kingston, RI, USA
Nissle-K	Nissle 1917 transformed with plasmid pBBR1MCS-2, conferring resistance to kanamycin
Nissle::Stx2PT	Nissle-K lysogenized with Stx2 phage from PT29S
PT29S	O157:H7 clinical isolate from CCHMC, a spontaneous streptomycin-resistant isolate (11)
EDL933	O157:H7 hamburger isolate (36), obtained from A. O’Brien
EDL933-G	EDL933 transformed with plasmid pBBR1MCS-5, conferring resistance to gentamicin
CFT073	Obtained from ATCC (WAM2267 ATCC 700928)
CFT073-G	CFT073 transformed with plasmid PBBR1MCS-5, conferring resistance to gentamicin