Proteus mirabilis Infection

Proteus mirabilis is a ubiquitous bacterium in the envi­ronment and can be isolated from the upper respiratory tract and feces of normal mice. Opportunistic infection resulting in disease has been observed in both immuno­competent and immunodeficient laboratory mice.

Suppurative pyelonephritis has been reported in male MM mice that are prone to development of diabe­tes, and nephritis has also been found in male C3H/HeJ mice. In SCID and SCID-beige mice, splenomegaly and multifocal hepatic lesions are typical macroscopic find­ings. In some cases, fibrinopurulent exudate may be present in the peritoneal cavity (Fig. 1.71). On micro­scopic examination, there are multifocal areas of coagu­lation necrosis in the subcapsular regions of the liver and around central veins, with minimal to moderate infiltra­tion with neutrophils. Septic thrombi may be present in vessels of tissues such as liver, intestinal serosa, and pancreas. Pulmonary lesions, when present, are charac­terized by serous flooding of alveoli and mobilization of

FIG. 1.71. Abdominal viscera of a SCID mouse with naturally occurring Proteus mirabilis septicemia. Note the irregular focal to coalescing hepatic lesions and the fibrinous exudate in the peritoneal cavity.

alveolar macrophages. Lung infection has also been found in NADPH oxidase deficient B6.129S6- Cybb^tm10m/J mice. In addition to the presence of histo­logical lesions consistent with bacterial sepsis, the recov­ery of large numbers of P. mirabilis from sites such as lung, liver, peritoneal cavity, and kidney will serve to confirm the diagnosis.