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

Health monitoring of rodent colonies has traditionally used live animal (LA) sampling by means such as the use of soiled bedding sentinels (SBS), with the associated expenditure of labor, supplies, and animals. In the spirit of the 3Rs, sentinel-free (SF) approaches are becoming more common. PCR testing of environmental samples is replacing traditional SBS-based testing for routine health monitoring of rodent colonies. Passive sampling of in-cage media exposed to pooled, soiled bedding is effective for detecting some common rodent pathogens. We hypothesized that PCR testing of commercially available media exposed to soiled bedding would be as effective as sampling SBS, or SBS combined with samples from colony animals, for detecting several enzootic organisms of mice (Mus musculus) within our facility. Media were placed in IVC cages and exposed to pooled dirty bedding from all cages on a rack side at biweekly cage changes during a 3-mo period. PCR results of the SF soiled bedding-exposed media were compared with results from feces, pelt, and oral swabs from SBS with and without SBS combined with 10 randomly sampled colony animals from the same rack side over the same period. Detection rates were similar for murine norovirus and Staphylococcus xylosus using SF testing compared with SBS with and without direct colony samples. Five organisms, Proteus mirabilis, Rodentibacter heylii, Staphylococcus aureus, Klebsiella oxytoca, and Klebsiella pneumoniae, were detected by SF testing, but not by LA samples. Demodex musculi, Entamoeba, Proteus mirabilis, Helicobacter spp., and Rodentibacter heylii were detected at significantly higher rates by SF testing compared with SBS with and without colony animal samples. SF testing detected organisms of zoonotic concern (S. aureus, K. pneumoniae) that were undetected by LA testing. SF testing detected organisms at similar rates during 2 consecutive quarters. We conclude that PCR testing of media exposed to pooled soiled bedding effectively detects these common enzootic organisms.