Gnotiobiotic and Axenic Animals

An important area of modern microbiology is to understand the way that consortia of microbes adapt to different habitats. A particularly important example of this, which is highly relevant to us as higher mammals, is the enormous number of commensal microbes that are present in our lower intestines. Whereas the microbial densities found in soils, or other geological or marine habitats, typically reach densities of up to 108 microbes per gram, the mammalian lower intestine is home to 1012 microbes per gram of luminal contents. These microbes therefore outnumber our own cells by an order of magnitude, and we constitute the best of good culture media. In order to determine the effect of these bacteria on the mammalian host animals must be maintained either entirely germ free (axenic) or with a limited defined microbiota (gnotobiotic). In this article, the methods of axenic and gnotobiotic animal research are described in detail.