Pseudomonas aeruginosa Infection

Pseudomonas aeruginosa is a nonspore-forming rod that is widespread in warm, moist environments, including water bottles and sipper tubes, which play a major role in mouse infections.

Epizootiology and Pathogenesis

Pseudomonas aeruginosa readily grows in water bottle sipper tubes, thereby facilitating cross-contamination among mice within a cage. Following procedures that impair granulocyte production and/or immune func­tion, including X-irradiation, cyclophosphamide treat­ment, or cortisone treatment, bacteremia is initiated when organisms penetrate nasal and oral mucous mem­branes. Following treatment with cyclophosphamide, bacteria are detectable at the nasal squamocolumnar junction and gingival epithelium, followed by invasion of regional lymph nodes and subsequent systemic dis­ease. Invasion of P. aeruginosa from the intestinal tract, particularly the cecum and colon, is another means of systemic infections. In one study, coinvasion with group B streptococci from the oral cavity may have facilitated the invasion of Pseudomonas into the systemic circula­tion. Similarly, disease with mortality in a colony of SCID mice was attributed to concurrent infections with enterococci and P. aeruginosa. There is mouse strain-related variation in susceptibility to experimental P. aeruginosa infections of the respiratory tract, with B6 and DBA/2 mice being susceptible, and BALB/c mice being relatively resistant. The increased susceptibility of some strains of mice was attributed to their inability to recruit large numbers of neutrophils and to a defect in tumor necrosis factor alpha production.

Pathology

Clinical signs may include listlessness, anorexia, con­junctivitis, nasal discharge, subcutaneous edema around the head, and acute death.

Diagnosis

Culture of the organism confirms the diagnosis. A his­tory of experimental procedures that impair the immune response and/or leukocyte function usually precedes the onset of outbreaks of systemic disease, in which P. aeruginosa may be recovered from internal organs and blood. Differential diagnoses include postimmuno­suppression deaths due to other opportunistic bacteria such as P. mirabilis, Enterobacter cloacae, K. oxytoca, and Enterococcus spp., which have also been shown to cause mortality in irradiated mice.