Comparing Mouse Health Monitoring Between Soiled-bedding Sentinel and Exhaust Air Dust Surveillance Programs

Abstract

To monitor rodent colony health in research facilities, soiled-bedding sentinel (SBS) animals have traditionally been used. SBS can be tested by various methods, which may include serology, PCR analysis, and necropsy. Several pathogens are unreliably detected by using SBS or transmitted poorly through soiled bedding, and collection and evaluation of SBS samples can be time-intensive. Recently, exhaust air dust (EAD) testing through PCR analysis has emerged as an adjunct or replacement method for rodent colony health monitoring. EAD monitoring may provide a more efficient, sensitive, and humane method for monitoring health status. Using both EAD and SBS health monitoring, we evaluated colony health over the course of 1 y in 3 research barrier rooms in which mice were housed exclusively on IVC racks. Three pathogens-Helicobacter spp., Rodentibacter spp. (previously Pasteurella pneumotropica), and murine norovirus (MNV)-were not excluded in 2 of the rooms, and we expected that these mice would test positive with some regularity. EAD monitoring was significantly more sensitive than SBS for detection of the bacterial agents. SBS failed to detect Helicobacter spp. at time points when EAD had 100% detection in the rooms that did not exclude the bacteria. The detection of MNV did not differ between health monitoring systems at any time point. The findings suggest that EAD is especially valuable in detecting bacteria poorly transmitted through soiled bedding. In addition, the corresponding results with MNV detection suggest that EAD surveillance can reliably be implemented as an alternative to SBS monitoring in a facility in which mice are housed exclusively on IVC racks.

Figure 1.

List of pathogens excluded from the Mouse Barrier Plus (MB+) room. All pathogens except those denoted by an asterisk are excluded from Mouse Barrier (MB) rooms. Sentinel serology was performed regarding pathogens in green; PCR analysis of sentinels was performed regarding pathogens in purple. The EAD filter was PCR-tested for all pathogens listed.

Figure 2.

(A) Diagram of room arrangement of both MB rooms. Sentinel cages with 2 mice per cage are indicated with green squares. There were a total of 20 sentinel cages between the 2 rooms. There were a total 16 racks between the 2 rooms: 12 single-sided racks and 4 double-sided racks. (B) Diagram of room arrangement of MB+ room. Sentinel cages with 2 mice per cage are indicated with green squares. There were a total of 7 sentinel cages and 6 total racks: 5 single-sided racks and 1 double-sided rack. BSC, biologic safety cabinet.

Figure 3.

(A) Front side of an IVC rack. Green arrows represent HEPA-filtered air coming in to each individual cage. Red arrows represent air exhausted out of each individual cage. (B) Back side of IVC rack, with representative arrows for the flow of air. Supply and exhaust plenum doors are seen on the left and right sides, respectively. (C) Close-up of open exhaust plenum door. Red arrow represents flow of exhaust air. Representative horizontal plenum is circled in red. The horizontal plenums were swabbed prior to initiation of study to confirm MB+-free status. Black arrow shows the vertical exhaust plenum with Sentinel Collection Media placed.

Figure 4.

(A) Sentinel EAD Collection Media. (B) Placement of Sentinel Collection Media into specifically designed holder to fit into vertical exhaust plenum of IVC rack. (C) Close-up of Sentinel Collection Media placed in vertical exhaust plenum, from above. (D) Collection of Sentinel Collection Media into sterile vial by using clean gloves.

Figure 5.

Proportion of IVC racks in MB rooms that tested positive for Helicobacter spp. by EAD or SBS each quarter. EAD identified Helicobacter spp. on every rack during all 4 quarters. EAD was significantly (†, P < 0.01) more sensitive in detection of Helicobacter spp. than SBS.

Figure 6.

Proportion of IVC racks in MB rooms that tested positive for Rodentibacter spp. by EAD or SBS each quarter. EAD was significantly (†, P < 0.01) more sensitive in detection of Rodentibacter spp. in each quarter than SBS.

Figure 7.

Proportion of IVC racks in MB rooms that tested positive for MNV by EAD or SBS each quarter. There was no significant difference (overall P > 0.5) in detection of MNV on each rack between EAD and SBS. Each EAD-positive result from a rack correlated with an SBS-positive result from the same rack.