Evaluation of Extended Sanitation Interval for Cage Top Components in Individually Ventilated Mouse Cages

Abstract

Sanitation frequency of mouse cage components can be determined through verification of microenvironment, including microbiologic load and air quality within the cage. Here we demonstrate a consistent microbiologic load on wire IVC lids that were used for as long as 8 continuous weeks to house 4 or 5 mice and significant decreases in the microbial load on filter tops at 4, 6, and 8 wk compared with 2 wk. In addition, air quality, represented by intracage ammonia concentration at the time of bedding change, did not differ between 2-, 4-, and 6-wk time points in cages containing same-sex groups of 4 or 5 male or female adult mice. We propose that the lack of significant differences represents justification for an extended sanitation frequency of as long as 6 wk for cage top components in mouse IVC housing and represents a performance standard that might be reproduced by similar facilities to determine appropriate sanitation frequencies for mouse caging components.

Figure 1.

Design and air movement in the IVC used in the current study. These IVC have HEPA-filtered air supplied through sealed shelf plenums into the cage, through air supply ports above the cage filter top. Air enters through the rear of the cage and exits at the front of the plenum. Water valves are located at the back of the shelf and enter the cage approximately 3.5 in. above the plastic floor through a manufacturer-installed grommet. This grommet is covered by a hinged door when not in use and is the access point for ammonia testing.

Figure 2.

Locations of microbiologic sampling points. Two 4 × 4-cm squares of the inner face of the filter top (sites A and B) and two 4-cm lengths of 5 bars of the wire lid (sites C and D) were sampled.

Figure 3.

Microbial load (no. of cfu) on cage top components. The median (point) and middle quartiles (bars) of each data set are indicated for each sample location (sites A, B, C, and D) across the 4 time points (2, 4, 6, and 8 wk). Significant differences were identified only for sample A, between the 2-wk time point and each of the other time points. P values as measured by Friedman testing are indicated where significance was identified.