rillions of commensal bacteria cover almost all environmentally exposed surfaces of our bodies at all times. But what are they doing? And why? If you want to understand the impact of commensal organisms on mammals, a good place to start is with mice that are devoid of all bacteria.
When I started working on this problem in 2002, so few people were still familiar with the germ-free mouse models that I had to persuade a retired research technician to help me set up sterile chambers and teach me the ways of “sanitary engineering.” Rather than the old steel and glass contraptions that he had used in his day (50 years ago), we were able to procure nicely modernized chambers with plastic bubbles that held up to four mouse cages. After my first few chamber contaminations, I began to understand why researchers rarely use germ-free animals.
Germ-free animals were conceived of ...
