FIG. 2.
Bacilli and spore loads in the lungs of mice challenged with aerosolized B. anthracis Sterne spores. Groups of A/J mice were exposed to aerosols of spores with an average pulmonary retained dose of 3 × 106 spores per mouse, and the number of CFU in the lungs of surviving mice was measured at days 1, 3, 5, 15, and 25 postchallenge. Germination gives rise to heat-sensitive vegetative bacilli and would be indicated by a reduction in the number of CFU in heat-treated (HT) versus untreated (UnT) samples. Therefore, a fraction of each lung homogenate was heat treated at 60°C for 30 min prior to diluting and plating. UnT CFU values are for spores and bacilli, HT CFU values are spores only.