Axenic

Axenic describes a biological system or environment that is free of all foreign life — not merely sterile in the sense of lacking pathogens, but completely devoid of microorganisms. The term is most commonly used in microbiology and immunology to describe germ-free animals raised in isolator systems, where even the air they breathe is filtered and the food they eat is sterilized.

The axenic condition is not a natural state but an experimental construct. It reveals the extent to which the host organism has become dependent on its microbiota for normal development and function. An axenic animal is not a baseline; it is a perturbation.