Germ-free animal

Germ-free organisms are multi-cellular organisms that have no microorganisms living in or on them. Such organisms are raised using various methods to control their exposure to viral, bacterial or parasitic agents. When known microbiota are introduced to a germ-free organism, it usually is referred to as a gnotobiotic organism, however technically speaking, germ-free organisms are also gnotobiotic because the status of their microbial community is known. Due to lacking a microbiome, many germ-free organisms exhibit health deficits such as defects in the immune system and difficulties with energy acquisition. Typically germ-free organisms are used in the study of a microbiome where careful control of outside contaminants is required.