Gastrointestinal structure and function in germ-free or gnotobiotic animals.

Gastrointestinal structure and function in germ-free or gnotobiotic animals A truly germ-free animal harbours no associated forms of life, including viruses. Occasionally the term 'germ-free' has been used in a more restricted sense to denote animals that are free of pathogens only. For this reason it is preferable to use the term 'axenic' or the more general term 'gnotobiotic', when referring to animals in which the composition of any associated fauna or flora (biota), if present, is fully defined. Gnotobiotic animals, unless deliberately contaminated, are bacteria free but may harbour congenitally transmitted agents such as the leukaemogenic virus, found in most strains of what are usually referred to as 'germ-free' mice.