STX2 and infection: To determine whether administration of Cip to JH2015-infected, Str-treated mice would increase Stx2 production in vivo and induce virulence as was previously observed by Zhang et al. for the Stx2-only producing O157:H7 strain 1:361 (Zhang et al., 2000), we gave Cip (5 μg/mouse) or phosphate-buffered saline (PBS) daily to JH2015-infected mice, beginning on day 2 post-infection until the end of the study.