FIG. 6.
Ability of secreted versus translocated hybrid YopE/LLO proteins to induce protective immunity against listeriosis in mice orally immunized with Y. pseudotuberculosis pIB155 carrying the indicated plasmid. Positive-control mice received a sublethal intraperitoneal dose of 5 × 103 CFU of Listeria 8 weeks prior to the challenge infection. Negative-control mice received the attenuated, nontransformed Yersinia carrier strain pIB155. Mice were intravenously challenged with 103 CFU of L. monocytogenes sv1/2a EGD 8 weeks after immunization. The bacterial load of spleens with L. monocytogenes was determined 72 h postinfection. Results are expressed as the mean log10 CFU ± standard deviation of 24 mice per group. The asterisk indicates a value that differs significantly from that of the negative-control group (*, P < 0.05).