Nonbacteremic Pseudomonas Pneumonia in Immunosuppressed Guinea Pigs

An experimental model of nonbacteremic pneumonia with a virulent strain of Pseudomonas aeruginosa was successfully established in guinea pigs immunosuppressed with cortisone acetate although the organisms were eliminated rapidly from the lungs without cortisone treatment. Using a pocket nebulizer, almost all the animals which received 10 6 organisms/g‐lung developed bronchopneumonia without any septic findings as long as 10 days after challenge. The lesions produced in such animals were characterized by dissemination of multiple purulogranulomatous changes. In the early stage of infection, infiltration of polymorphonuclear cells (PMNs) in the bronchiolar and alveolar spaces was diffuse, later showing multifocal accumulation with the formation of central spherical grains enclosing bacterial colonies. In the later stage, granulation tissue consisting of large mononuclear cells, fibroblasts and collagen fibers developed around the PMN accumulation. The animals which received 10 7 organisms/g‐lung, on the other hand, developed severe pulmonary hemorrhages and necrosis followed by septic death.