Improved Detection of Murine Pathogens Using Sentinel-Free Media Compared to Live Animal Sampling

Area of Science:

• Veterinary Pathology
• Microbiology
• Animal Health Monitoring

Background:

• Traditional rodent colony health monitoring relies on live animal (LA) sampling, including soiled bedding sentinels (SBS), which is labor-intensive and uses resources and animals.
• Sentinel-free (SF) approaches, such as PCR testing of environmental samples, are increasingly adopted, aligning with the 3Rs principles (Replacement, Reduction, Refinement).
• Passive sampling of in-cage media exposed to soiled bedding shows promise for detecting common rodent pathogens.

Purpose of the Study:

• To evaluate the efficacy of PCR testing commercially available media exposed to soiled bedding as a sentinel-free method for detecting enzootic organisms in mouse colonies.
• To compare the diagnostic performance of SF testing with traditional SBS sampling and direct colony animal sampling.

Main Methods:

• Commercially available media were placed in IVC cages and exposed to pooled soiled bedding biweekly over 3 months.
• PCR testing of SF media was compared with results from feces, pelt, and oral swabs from SBS, with and without direct sampling of colony animals.
• Detection rates of various enzootic organisms were analyzed.

Main Results:

• SF testing showed similar detection rates for murine norovirus and Staphylococcus xylosus compared to SBS methods.
• SF testing detected five organisms (Proteus mirabilis, Rodentibacter heylii, Staphylococcus aureus, Klebsiella oxytoca, K. pneumoniae) not identified by LA sampling.
• SF testing identified Demodex musculi, Entamoeba, P. mirabilis, Helicobacter spp., and R. heylii at significantly higher rates than SBS methods and detected zoonotic pathogens (S. aureus, K. pneumoniae) missed by LA testing.

Conclusions:

• PCR testing of media exposed to pooled soiled bedding is an effective sentinel-free method for detecting common enzootic rodent organisms.
• SF testing offers comparable or superior detection rates to traditional methods, including for organisms of zoonotic concern.
• This approach aligns with the 3Rs by reducing reliance on live animal sampling for routine health monitoring.