Pseudomonas aeruginosa Infection: Pseudomoniasis

Pseudomonas aeruginosa is an opportunistic Gram-nega­tive bacillus that contaminates a variety of environ­ments, including food, bedding, water bottles, bottle stoppers, and sipper tubes.

Pathology

In acute cases, there may be pulmonary edema, spleno­megaly, and visceral ecchymoses, consistent with a Gram-negative bacterial septicemia. In rats that succumb during the subacute to chronic stages of the disease, multifocal necrosis with abscessation may be present in organs such as lung, spleen, and kidney. In animals with indwelling jugular catheters, vegetative lesions may be present on the tricuspid valves. On microscopic examination, lesions in acute cases are those of an acute bacterial septicemia, with vasculitis, thrombosis, hem­orrhage, and polymorphonuclear leukocyte infiltration. In affected foci, changes vary from acute coagulative necrosis to suppuration, with obliteration of the normal architecture. Lesions are usually most extensive in the lung. In addition to thromboembolic changes with hem­orrhage, bacterial colonies and proteinaceous fluid are frequently present in alveoli.

Diagnosis

The history of procedures that induce neutropenia or certain surgical manipulations, coupled with typical gross and microscopic changes, should be sufficient to provide a provisional diagnosis. The Gram-negative organisms are usually identifiable in sections stained with tissue Gram stains. The organism can usually be recovered from heart blood or spleen in septicemic animals. In subacute to chronic cases, P. aeruginosa may be isolated from visceral lesions. Differential diagnoses include visceral abscessa­tion due to C. kutscheri or P. pneumotropica infections, salmonellosis, and pulmonary abscessation associated with chronic respiratory disease.