axenic

Axenic describes systems or organisms that are free from any other living organisms. In microbiology and laboratory sciences, an axenic culture contains only a single species and is maintained in a sterile environment to prevent contamination. The term is distinct from sterile, which means no viable microorganisms present, but axenic specifically focuses on the absence of unintended cohabitants in a biological system. The concept is central to studies of host–microbe interactions, cell biology, and experimental ecology.

Common uses include axenic cell cultures (animal or plant cells grown in sterile conditions), axenic microbial cultures used to study a single species, and axenic animals (germ-free or axenic organisms) used to assess the role of microbiota. Related terms: germ-free is often used synonymously with axenic; gnotobiotic refers to an axenic system in which any present microorganisms are known.

How axenity is achieved involves strict aseptic technique and sterilization of media (autoclaving, filtration), instruments, and workspaces, often within laminar-flow hoods or closed barrier systems. Verification methods include routine culturing to detect contamination and molecular approaches (PCR, sequencing) to detect low-abundance organisms.

Limitations include the difficulty of guaranteeing complete axenity, as some endosymbionts or dormant forms can escape detection. Additionally, maintaining axenic conditions can alter host physiology or influence experimental outcomes, potentially affecting the generalizability of results.