Figure 1. Organ dissemination of the wild type Vollum strain and the toxins-less mutant in PA immunized Guinea pigs.

Guinea pigs were immunized with alum absorbed PA at time 0 and 4 weeks and challenged at week 6 by intranasal instillation of spores (10⁷ CFU – 500 LD₅₀ of the WT strain and 10⁸ CFU – 2 LD₅₀ of the toxins deficient mutant strain). Serum αPA titers were higher than 100,000. Bacterial burden were determined post mortem at various tissues of individual animals.