Source: The Free Dictionary, Wikipedia, Association for Gnotobiotics.

Axenic: (adj.) (Greek, xenikos: foreign) not contaminated by or associated with any other living organisms; not contaminated by or completely free of the presence of other organisms; ‘an axenic culture’ (of experimental animals) raised under sterile conditions; ‘axenic conditions’; ‘germ-free animals’. Same meaning as ‘germ-free’.

Germ-free: (adj.) free from germs or pathogenic organisms; free of microorganisms; sterile; ‘a germ-free environment’. Same meaning as ‘axenic’.

Gnotobiology: the study of organisms or conditions that are either free of germs or associated only with known or specified germs.

Gnotobiosis: (Greek: known life) a condition in which all the forms of life present within an organism can be accounted for. Typically these organisms are germ-free or gnotophoric (having only one contaminant).


  1. of or relating to gnotobiology.
  2. free of germs or associated only with known or specified germs.

The recently accepted definition of ‘gnotobiote’ as put forth by the International Committee on Standardized Genetic Nomenclature for Mice is: ‘Animal strains derived by aseptic surgical procedures or from sterile hatching of eggs, which are reared and maintained with germ-free techniques under isolator conditions and in which the composition of the associated fauna and flora, if present, is fully defined by accepted current methodology.’ (Association for Gnotobiotics).

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