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The science involved with maintaining a microbiologically controlled environment, and with the knowledge necessary to obtain and use biological specimens in this environment. The roots of the word are gnotos, meaning well known, and biota, the combined flora and fauna of a region.
All exposed surfaces of an animal are teeming with microbes. For example, the contents of the large intestine may contain 3 trillion microbes per ounce (100 billion per gram), belonging to several hundred species. Even if the animal itself is the primary interest of a researcher, there is no direct way to determine how many of an animal's normal characteristics are truly its own, and how many involve interaction with or reaction against resident microbiota. The only way to determine this is comparison with animals that have no microbiota. If differences are found, then the role of individual microbial species can be studied by inoculating pure cultures of these species into the animals without a microbiota.
Thus, gnotobiotics evolved initially to answer questions about what difference the resident microbiota makes, and which members of the microbiota make the difference. Answers become more and more essential in going beyond the effects of pathogenic microbes to the harmful or helpful long-term effects of environmental chemicals, compounds produced in the host's own metabolism, and therapeutic drugs being tested for efficacy, toxicity, or carcinogenicity. The activity of the microbiota is proportionately much greater in laboratory animals than it is in humans, and could have a decisive effect on such chemicals, especially since the chemicals are often received in small doses. For example, intestinal microbes turn a minor component of the cycad bean, a South Pacific foodstuff, into a carcinogen. One of the best drugs against parasitic schistosomes in humans is turned into a carcinogen by a single species of intestinal streptococcus. Gnotobiotic studies are designed to detect such possibilities.
Gnotobiote is the term applied to an animal (or plant) with a defined microbiota. The most simple of gnotobiotes is the animal with no microbiota. Invertebrate animals of this type are most frequently called axenic. Vertebrate animals may also be called axenic, but are more frequently called germfree. Gnotobiology is a term sometimes used to designate studies involving gnotobiotes, although it tends to suggest that there is a unified body of knowledge which results from studying gnotobiotes. In fact, the gnotobiote is a more precisely defined laboratory animal which helps elucidate biological phenomena in immunology, nutrition, physiology, oncology, gastroenterology, microbial ecology, gerontology, pathogenic microbiology, parasitology, and so on.
gnotobiology, a branch of experimental biology that includes the production and raising of laboratory animals whose bodies are free either of all microorganisms (including bacteria, viruses, protozoans) and helminths and arthropods (so-called sterile animals) or merely of certain pathogenic species of them (so-called gnotobiotic animals). Gnotobiotics arose with the requirements of morphology, physiology, genetics, microbiology, medicine, veterinary medicine, and other sciences.