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GNOTOBIOTIC ANIMALS
Gnotobiotic animals, also known as germ-free animals, are laboratory animals that are completely free of all known and detectable microorganisms, including bacteria, viruses, fungi, and parasites. These animals are maintained in highly controlled and sterile environments to study the effects of specific microorganisms or to investigate the interactions between the host and the microbiota.
The demonstration that laboratory animals can be reared and reproduce in a sterile environment made it possible to consider the more extensive use of this method. At present time, germ free rats, mice etc. are reared in many laboratories. Such animals were earlier called microbe-free or germ free animals but latter, these names were dropped and the name gnotobiotes was used. Gnotobiotic animals may be free from one or all forms of microbes:
- Axenic gnotobiotesare those animals that are totally free from all microorganisms
- Monoaxenic gnotobiotesare those animals in which only one particular type of microorganism have been eliminated.
- Diaxenic gnotobiotesanimals are those that two types of microorganisms have been eliminate.
- Heteroaxenicgnotobiotesare those in which microorganisms affecting the animals have been modified while those animals having unmodified microbiota are called conventional animals
Characteristics of Gnotobiotes
Gnotobiotes have different characteristics from conventional animals. they reproduce equally well without microbes , the growth rate is within the normal range but however the humoral and cellular defense systems is not as developed as in conventional animals . However, both systems respond in a characteristic fashion following stimulation with antigens
Most gnotobiotes have distended caecum which may be about 30% of the body weight .This can impair reproduction in these animals and may become twisted in older rats and mice causing death . The enlarged caecum and bowels have high moisture content in gnotobiotes. These is mainly due to lack of microorganisms in the mecum that are responsible for the degradation of endogenous proteins, mucopolysacharides and other substances which are produced by cells lining the alimentary canal
Uses of Gnotobiotes.
The probable use of gnotobiotes include:
- They may be used in studies aimed at determining their development and reactions in relation to a diet that have been chemically defined
- They also serve as sources of sterile organs and tissues for cultivation.
- They provide good tools for research especially in studies involving the study of immune system.
- When associated with one or more pure cultures , they give an opportunity for a more critical study of the etiology of infectious disease
- Gnotobiotes give a more uniform susceptibility than those that have been previously infected
- They are normally used in the production of colonies or herds of animals that are free from one or more specific agent
Before maintaining or using gnotobiotes, it is necessary to confirm their biological status to ensure that they are free from all other living forms. Procedures for testing these should be modified from time to time to reduce incidences of undetected microorganisms. New methods should be used as soon as they are approved.