Axenic culture

Definition

A culture containing only a single species, strain, or variety of organism and entirely free of all other living contaminants, including bacteria, fungi, and other microbes. In entomology and arachnology, axenic culture is essential for isolating the effects of host genotype, verifying Koch's postulates for entomopathogens, and studying obligate symbionts or gut microbiome function by comparing axenic and gnotobiotic (known microbiome) individuals.

Etymology

Greek a- (without) + xenos (stranger, foreigner), referring to the absence of foreign organisms

Example

Researchers reared axenic cultures of Drosophila melanogaster to demonstrate that specific gut bacteria were required for proper immune priming against fungal pathogens, by comparing germ-free flies with those inoculated with known microbial communities.

Synonyms

• germ-free culture
• sterile culture

Related Terms

• gnotobiotic
• monoxenic culture
• microbiome
• Symbiosis
• Koch's postulates
• entomopathogen
• dysbiosis

Usage Notes

Distinguish from 'monoxenic culture,' which contains one known species plus its associated symbionts or parasites. 'Axenic' is absolute—any detectable contaminant invalidates the designation. In practice, achieving true axenic conditions with multicellular arthropods is challenging; surface sterilization of eggs and rearing on autoclaved diet are standard but imperfect methods. The term is sometimes loosely applied to 'bacteria-free' cultures that may still harbor undetected fungi or viruses.