Fig. 2
Fifty percent lethal dose (LD50) estimation. Using the dose-response experiments, we estimated LD50 values and 95 % confidence intervals for the wild-type strain and each of the mutant strains. The estimated wild-type LD50 of 2.62 CFU, where CFU denote colony-forming units, agreed with previously estimated values for the wild-type F. tularensis subsp. tularensis Schu S4 strain. The estimated LD50 values for ΔFTT0482c and ΔFTT1597 were higher than the wild-type value and outside its 95 % confidence intervals, whereas the LD50 value estimated for ΔFTT1538c was above the wild-type value, although with overlapping confidence intervals. These results support the notion that ΔFTT0482c, ΔFTT1538c, and ΔFTT1597 attenuate F. tularensis virulence in this animal model