Axenic (Gnotobiotic) Animals

Axenic animals are laboratory controlled animals that are germ-free i.e., animals that are not contaminated with any microorganisms and are devoid of any microflora. Such animals can also be called Gnotobiotic animals. Gnotobiotic or Axenic animals have tremendous medical research applications. The microflora from axenic animals help scientists to elucidate the relationship that exist between disease and pathogens; and they do this by comparing pathogens with organisms isolated from gnotobiotic animals.

Laboratory animals that are gnotobiotic normally contain a known amount of microbiota and, such animals are usually raised in the laboratory for medical research purposes. Axenic animals are good experimental models for the investigation of the interaction between specific microbes and animals. They serve as sources of pure cultures for in vivo microbiological research.

A microbiologically monitored environment in the microbiology laboratory can also be referred to as an axenic or gnotobiotic environment. To establish a gnotobiotic animal (e.g., mice, rat, rabbits or monkeys) in the laboratory, the pregnant female animal is delivered of its foetus by a caesarian section in aseptic conditions (e.g. in a sterile isolator), and the young animal (to be made gnotobiotic) is immediately transferred to a germ-free environment where it is raised. The germ free environment (sterile isolator) ensures that all food, air, water and other substances entering it are sterile. This assures that the isolator is totally germ-free.

Gnotobiosis is a condition in which all the forms of life present within an organism can be accounted for. Gnotobiotic animals including gnotobiotic mice, rats, monkeys and dogs or cats are valued for the study of infectious diseases wherein the clinical signs and lesions of disease can be directly related to host pathogen interactions as is obtainable in the human body. Such animals provide a suitable environment for the maintenance of organisms raised in niches where the effects of environmental factors and other confounding physiological factors do not interfere or affect their development.

A colony of gnotobiotic animals is maintained by ensuring mating among the female and male gnotobiotic animals generated. The waste products of gnotobiotic animals, the exhaust air from their isolators and samples are subjected to periodic bacteriologic examination in order to ensure that the environment is still germ free. Such a microbiological test must produce no colony or growth of microorganism in order to authenticate the isolator as truly gnotobiotic. Gnotobiotic animals as aforementioned are usually cesarian-derived (i.e., through operation) under aseptic conditions and raised in germ-free (GF) environmental conditions such as isolators.

Gnotobiotic animals are free from all types of organisms or normal flora. However, gnotobiotic animals can be allowed to assume or take up certain type of microflora through a process of experimental colonization. This type of experimental colonization of gnotobiotic animals can be achieved by a set of known or defined bacterial species such as Altered Schaedler’s Flora (ASF). The Altered Schaedler flora (ASF) is a community of eight bacterial species including two Lactobacilli, one Bacteroides, one spiral bacteria of the Flexistipes genus, and four extremely oxygen sensitive (EOS) Fusobacterium species. ASF are used to study a variety of activities involving the intestinal tract of humans or animals such as gut microbiome community, immunity, metabolism, inflammation, diseases and pathogenesis or disease virulence.


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