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.

Testing Alternative Surface Disinfection Agents for Zebrafish (Danio rerio) Embryos.

Pathogen transmission into zebrafish colonies is controlled through vigilant biosecurity practices. One such practice is embryo surface disinfection, which often uses sodium hypochlorite. However, if sodium hypochlorite is used at an inappropriate pH, concentration, or exposure time, zebrafish embryos can experience significant mortality and morbidity. Reagent-grade sodium hypochlorite is often used for embryo surface disinfection because commercial-grade sodium hypochlorite has additional ingredients that may have deleterious effects on the embryo. In addition, chlorine dioxide and the combination of sodium chloride and potassium peroxymonosulfate (SCPP) are effective equipment disinfectants; however, the effects of these chemical agents on zebrafish embryos during surface disinfection are unknown. In this study, we exposed strain 5D zebrafish embryos (ages, 6 and 24 h postfertilization) to 4 chlorine-containing agents (reagent-grade sodium hypochlorite [bleach], commercial-grade sodium hypochlorite [bleach], SCPP, and chlorine dioxide) at either 50- or 100- ppm for 5 or 10 min. All groups were evaluated at 5 d postfertilization for survival, hatching rate, and morphologic defect rate. The experimental group with the highest survival and hatching rates and the lowest morphologic defect rate was the 24-h postfertilization embryos exposed to 50 ppm SCPP for 5 min. The survival, hatching rate, and defect rate did not differ significantly among age-matched controls; however, the hatching rate after exposure to 50 ppm SCPP was significantly higher than that of embryos exposed to 50 ppm reagent-grade sodium hypochlorite for 5 min (100% compared with 23% respectively). SCPP solution may provide an alternative surface disinfectant for zebrafish embryos because it maximizes survival and hatching rates and minimizes morphologic defect rates. However, in vivo efficacy against common zebrafish pathogens requires further testing. Use of chlorine dioxide at 50 ppm or greater is not recommended for zebrafish embryo surface disinfection due to significant mortality among 6 and 24 h postfertilization embryos.