Fig. 3.
Ty21a-PA-01 protects mice from lethal spore challenge. Mice were immunized three times with 5 × 107 CFU of Ty21a control (filled triangles) or Ty21a-PA-01 (open squares) by the IP route and were challenged two weeks after dose 3 with Sterne spores at a dose of 4.9 LD50 by intranasal installation and monitored twice daily for 21 days. Mean time to death (TTD) was calculated for the controls. As noted, 1 of 10 control mice immunized with Ty21a and 20/20 mice immunized with Ty21a-PA-01 survived (p = 2.2 × 10−8, Fisher’s exact test, two-tailed). For the nine control mice that died, the mean TTD was 4.2 ± 0.1 (mean ± SD) days