TABLE 1.

Bacterial strains used in this study

Strain	Relevant characteristic(s)	Reference(s)
Y. enterocolitica 8081	Biotype 1B, serotype O:8	23
Y. enterocolitica 8081u−	Y. enterocolitica 8081 ureF::Kmr	4
S. enterica serovar Typhimurium SL1344	Resistant to streptomycin	11
C. rodentium ICC169	Resistant to nalidixic acid	7, 37
C. perfringens JIR4472	SM101(pJIR1841), spore forming, resistant to chloramphenicol	V. Adams, D. Lyras, and J. I. Rood, unpublished