Figure 6.

Bactericidal activity of mice immunized with Vi vaccines over time and the effect on protection. C57Bl/6 mice were immunized i.p with PBS, 4 µg Vi-PS, on day 0, or 2 µg Vi-CRM₁₉₇ or Vi-TT at both day 0 and 35. (A) Serum bactericidal activity of sera collected day 185 (6 months post-primary immunization) was measured against TH177, represented as mean change from the starting LogCFU/mL bacterial dose over time, normalised to the negative control values at each timepoint. Complete human serum (CHS) was used as a positive control. Error bars represent SEM. (B) Serum bactericidal activity from the 180-minute timepoint represented as mean change from the starting LogCFU/mL between mice immunized once at day 0 with Vi-PS. or twice at day 0 and 35 with Vi-CRM₁₉₇ or Vi-TT. (C) Spleen or (D) Liver colony forming units (CFU) of C57Bl/6 (WT) mice immunized i.p with 4 µg Vi-PS or PBS on day 0, or 2 µg Vi-TT at both day 0 and 35 then infected for 24 hours with 1x10⁵ CFU Vi+ S. Typhimurium TH177 at day 154 or 201 (5 or 7 months post-primary immunization). Representative of 2 experiments with n = 4 or 5 mice/group. For B-D each point represents data from one mouse. Serum bactericidal activity of sera taken day 199 (prior to day 202 infection), represented as change from the starting LogCFU/mL bacterial dose normalised to the negative control values at each timepoint, or at the 180 minuet timepoint alone. Complete human serum (CHS) was used as a positive control. Groups contain 4-5 mice/group and in the right hand graph each point represents one serum. *p≤0.05, ***p≤0.005, and ns = non-significant by Mann-Whitney U test between individual groups (two-tailed).