Long-term Maintenance of Sterility Following Skin Transplantation in Germ-free Mice

There is considerable interest in investigating the role of the microbiota in various diseases, including transplant rejection. Germ-free (GF) and gnotobiotic mice are powerful models for this line of investigation, but performing surgery within the confines of a sterile housing isolator is exceptionally challenging. Development of rigorous protocols to be able to remove axenic mice from their sterile isolator for surgical intervention in a Class II biological safety cabinet (BSC) without compromising sterility would give many investigators access to this model and broaden possible studies. However, it is assumed that GF animals will most often become colonized with environmental microbiota upon leaving the isolator. In this study, we tested whether applying sterile techniques for animal transport out of the isolator and skin transplantation in a Class II BSC could maintain animal sterility. Quantitative polymerase chain reaction (qPCR) of the bacterial 16S ribosomal RNA gene, and cultures in various aerobic and anaerobic conditions were used to probe for bacterial contamination before and after transplantation. Out of 28 surgeries performed, only 3 mice acquired bacterial contamination coincident with a transient shutdown of the ventilation system in the BSC. Our results indicate that skin transplantation can be successfully performed in GF mice using sterile conditions for transport and surgery in a Class II BSC, but requires continuous positive airflow. Our approach paves the way to investigating the role of the microbiota in modulating immune responses to skin allografts as a first model of solid organ transplantation in GF mice.