Figure 3. Analysis of vaccination efficacy of M15 S. Typhimurium strain. Vaccinated C57BL/6 mice groups (PBS, n = 5; MT12, n = 5; MT15, n = 5) were ampicillin-treated (25 mg by gavage), challenged with wild-type SB300 (amp^r, sm^r) after 24 h of treatment, and euthanized at day 4 post-challenge (p.c.). (A) Colonization of SB300 at various host sites after challenge. (B) Enumeration of cecal pathology in terms numerical pathoscore was determined as described in material and methods section. Broken lines in the graphs shows minimum detection limit. n.s., not significant; *statistically significant (P < 0.05, t test). (C) Representative HE-stained cecal sections obtained from SB300-challenged mice groups pre-immunized with MT12, MT15, and PBS (control). Bar, 200 µm. S, submucosal edema; Lp, lamina propria; L, lumen.