Bacterial and spore burden in the lungs of mice infected with toxin-deficient B. anthracis mutants.

Mice were inoculated i.n. with ∼1.5×10⁷ spores. Lungs were harvested at 2 and 4 weeks post inoculation, homogenized and plated with or without heat treatment. The results were combined from two independent experiments. Closed circles represent total viable bacteria and open circles heat-resistant dormant spores.