Effect of non-sterile bedding and feed on the spread of some infectious agents among BALB/c mice in SPF animal housing

The aim of this study was to identify and assess the risk of spreading infectious agents in a colony of specific pathogen free (SPF) BALB/cOlaHsd mice when using non-sterile bedding and feed. The total number of microbial colonies in bedding was estimated, and their species identification was carried out using bacteriological methods. Infectious agents regulated for SPF mice were determined in the mouth and fecal swabs of mice using real time PCR. The mice in the animal facility were housed in individually ventilated cages (IVC). To assess the effect of air, one group of animals was kept in open-air cages (OAC). The study duration was 90 days. Staphylococcus epidermidis was identified in bedding in the groups of animals that were kept on non-sterilized bedding and in OAC. In addition, the level of bacterial contamination in the group with non-sterile bedding was significantly higher (1065 CFU/g) than the control group and higher than the other groups. These microorganisms in bedding were Lactobacillus spp, Staphylococcus spp and Escherichia coli. Staphylococcus spp and E.coli are not commensal microflora, but can be found in SPF animals. As a result of PCR testing, only Rodentibacter pneumotropicus was found in the mice; it was present in each group. It is assumed that the mouse colony was initially contaminated with this infectious agent. No visible pathological changes such as enlargement of the spleen, liver and lymph nodes, or intestinal distension, were detected at necropsy. The results of this study showed that personnel are possibly the main source of S. epidermidis because this microorganism is not found in SPF-mice. The transfer of bacterial agents occurs mainly through poor-quality bedding, as well as by the air.