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.