Germfree Animal

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germfree animal

[′jərm‚frē ′an·ə·məl]
An animal having no demonstrable, viable microorganisms living in intimate association with it.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Germfree Animal


an animal free of macroparasites and all microorganisms, including viruses.

Attempts were made to raise germfree animals in the late 19th century, after L. Pasteur posed the very important question of whether there can be microbeless animal life. It was only in the late 1940’s that the American scientist J. Reyniers and his coworkers developed adequate germfree diets and apparatus with which they were able to demonstrate that artificial conditions may be created that favor the growth and reproduction of germfree animals. The use of germfree animals in immunology, bacteriology, virology, parasitology, and other fields of experimental biology and medicine has proven to be extremely fruitful, leading to the establishment of an independent scientific discipline—gnotobiology—in the 1960’s. The techniques and principles of gnotobiology are also used in clinical medicine to completely isolate an operative wound and the individual from the surrounding microflora.

A germfree animal is obtained by the aseptic extraction of a fetus from the uterus (hysterotomy, hysterectomy) or by incubating the sterilized eggs of insects or birds and then raising the animals in special isolators. A germfree animal may be obtained only if the fetus was germfree. After birth, under natural conditions all animals and man become hosts to a normal microflora, which is present in the upper respiratory and gastrointestinal tracts and on the skin and other parts of the body exposed to the outside. Comparative experiments are performed on conventional and germfree animals to determine the role of microfioral organisms in the vital activities of a host. Animals that are germfree differ from those raised under natural conditions in structure (microscopic and macroscopic) and in the functioning of chiefly those organs and tissues that would normally be in contact with microflora.

A knowledge of the characteristics of germfree animals is important in studying the causation of immunity, the variation of certain bacterial species, digestion, and the infectious process under strictly controlled conditions and in the absence of normal microflora. Gnotobiologists have discovered that under natural conditions symbiosis with normal microflora is essential for host organisms in order for the latter to obtain vitamins, amino acids, digestive enzymes, and other substances. Depending on the adequacy of germfree diets, germfree animals may develop as well as or more poorly than conventional animals. Some animal species, for example, hamsters, have not yet been raised under germfree conditions.

Germfree-research, or gnotobiology, laboratories were established in the 1930’s in the USA, Japan, and Sweden and later in Great Britain, France, the Netherlands, the Federal Republic of Germany, Belgium, Czechoslovakia, the Polish People’s Republic, and the Hungarian People’s Republic. In the USSR, germ-free animals were first obtained in 1966 at the Institute of Epidemiology and Microbiology of the Academy of Medical Sciences of the USSR, where the first gnotobiology laboratory was established.


Chakhava, O. V. Gnotobiologiia. Moscow, 1972.
Luckey, T. D. Germfree Life and Gnotobiology. New York-London, 1963.
Advances in Germfree Research and Gnotobiology. Cleveland-London, 1968.
The Germfree Animal in Research. London-New York, 1968.
Germfree Research: Biological Effect of Gnotobiotic Environments. New York-London, 1973.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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Mazmanian's team treated the germ-free animals with individual strains of those microbes.
(11) However, in another study using a rodent model of autism, researchers showed it was possible to reverse deficits in social interactions by colonizing the initially germ-free animals with the beneficial bacterium Bacteroides fragilis.
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The sterile environment allows researchers to compare germ-free animals with those raised normally.
Studies of germ-free animals are difficult to interpret and translate to humans, due to major variabilities in GI function among animals and humans, as well as immune function, and other effects on the brain.
Germ-free animals have extensive deficits in the development of the gut-associated lymphoid tissues (GALT) and defects in antibody production.[sup][29],[30] Compared to animals housed under specific pathogen-free conditions, germ-free mice have underdeveloped GALT including Peyer's patches and mesenteric lymph nodes.
Peanuts revved up the germ-free animals' immune systems, but mice with normal gut bacteria didn't have the bad reaction.
"These germ-free animals are leaner than animals that are colonized with a complex microbial community, even though they eat more food," says Peter Turnbaugh of Harvard University's FAS Center for Systems Biology.
One way to explore the significance of bacteria to the mammalian supraorganism is to look at germ-free animals since they have to go it alone without a microbial community to support them.