Efficacy of filter top cages to reduce cross-contamination in mice housed in experimental facilities

Abstract

An optimal microbiological status is key to ensuring reproducible experimental results. However, contamination is difficult to avoid during long experimental procedures when animals spend time outside their enclosures, in contact with users and different equipment. To evaluate the efficacy of filter-top cages to minimize cross contamination when experimental mice of different microbiological status share the same room, we studied a complete panel of microorganisms in mice housed in different systems. C57BL6/N mice were purchased to an SPF facility: one group was housed in filter top cages whereas another group stayed in similar cages but without the filter-top. These external mice shared the room with mice involved in other experimental protocols between 8 and 13 weeks. A group of conventional mice born at our facilities housed in open cages served as control. Samples from different organs were analyzed by PCR. Mice born at the experimental facility were positive for several bacteria, virus, and parasites. All the bacteria present in this control group, were also found in the group of mice originally SPF housed in the open cages. Only 2 out of the 6 viruses present in the facilities were transmitted to the external mice in open cages, whereas no parasites were detected. Interestingly, mice housed in the filter-top system only recovered 3 bacteria from all the microorganism present in the facilities. Our results shown that using filter-top cages for long periods may be a refinement tool when there is no alternative to share the room with mice of different microbiological status.