FIG. 3.
Bacilli and spore load in distal organs 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. The numbers of CFU in the liver and spleen (A) and pulmonary draining lymph nodes (hilal and mediastinal) (B) were measured on days 1, 3, and 5 postchallenge. Germination of spores gives rise to heat-sensitive bacilli. To determine CFU resulting from spores or spores plus bacilli, a fraction of each homogenate was heat treated (HT) at 60°C for 30 min prior to diluting and plating. Untreated (UnT) CFU values are for spores and bacilli, whereas HT CFU values are spores only. Counts for the liver represent CFU in 300 mg of tissue and counts for the spleen represent total organ CFU. Counts for lymph nodes are CFU/ml of tissue homogenate. The limits of detection were 250 CFU for the liver and spleen and 10 CFU for the lymph nodes.