Figure 3. Survival profiles of mice, guinea pigs and rabbits infected subcutaneously with the Sterne and SterneΔhtrA strains.

The animal groups (10 ICR mice, 20 guinea pigs or 5 rabbits per experimental group) were inoculated via the SC route with increasing spore doses of the parental Sterne strain (black circles), the mutated SterneΔhtrA strain (white squares) and the transcomplemented SterneΔhtrA/HtrA strain (tested in mice grey diamonds/grey dotted line). The survival of the animals was followed for 3 weeks. Table 2 shows the LD₅₀ values calculated for the various strains in the three animal models. The experiments described employed the SterneΔhtrA IIBR-BA106 strain, but similar results were observed with the SterneΔhtrA IIBR-BA104K^R strain (not shown). In the guinea pig experiment, 19 of 20 animals survived a dose of 10⁹ SterneΔhtrA spores, but all the animals survived a dose of 10¹⁰ spores.