Detection and Transmission of Proteus mirabilis in Immunodeficient Mice

The exclusion of opportunistic pathogens is important for protecting animal health and ensuring desired research outcomes in highly immunodeficient mice. Proteus mirabilis has been associated with gastrointestinal tract lesions, septicemia, pyelonephritis, splenomegaly, and hepatitis and can influence select mouse models. To inform health-surveillance practices after we experienced difficulty in excluding P. mirabilis from our mouse colony, we aimed to determine the likelihood of detecting P. mirabilis-positive immunocompromised (SRG), immunovague (Fbn1^+/-), and immunocompetent (CD1) colony mice through culture and PCR testing; to evaluate transmission via 2 sentinel-based approaches (direct contact and indirect dirty-bedding transfer); and to further characterize associated pathology. We hypothesized that immunocompromised mice would be better detectors and transmitters of P. mirabilis. Multiple logistic regression models were used for analysis and included PCR copy number, repeated testing, age, sex, and antibiotic-treated (trimethoprim-sulfamethoxazole) diet as covariates. Repeated testing over 10 wk showed that P. mirabilis -colonized immunocompromised colony mice were 95 times more likely than immunocompetent mice to test positive by culture and 30 times more likely by PCR assay. Sentinel mice were 15 times more likely to test positive by PCR assay for P. mirabilis when exposed by direct contact compared with dirty bedding and 18 times more likely to test positive when exposed to positive immunocompromised as compared with immunocompetent colony mice. After 10 wk of exposure, 3.8% of dirty-bedding sentinel PCR tests were positive, as compared with 30.7% of contact sentinels. Only immunocompromised mice on antibiotic diet (37.5%) developed lesions of the urogenital tract and abdominal cavity consistent with known pathology of P. mirabilis. Our findings suggest that PCR testing of dirty-bedding sentinels alone is not sufficient for the detection of P. mirabilis in mouse colonies. Direct-contact sentinels and testing of colony mice-especially if immunocompromised-with adjunct culture may facilitate successful bioexclusion.