Gnotobiosis (from Greek roots gnostos 'known' and bios 'life') is a condition in which all the forms of life present within an organism can be accounted for. Typically gnotobiotic organisms are germfree or gnotophoric (having only one contaminant).
A gnotobiotic animal is an animal in which only certain known strains of bacteria and other microorganisms are present. Technically, the term also includes germ-free animals, as the status of their microbial communities is also known. However, the term gnotobiotic is often incorrectly contrasted with germ-free.
Gnotobiotic animals (also 'gnotobiotes' or 'gnotobionts') are born in aseptic conditions, which may include removal from the mother by Caesarean section and immediate transfer of the newborn to an isolator where all incoming air, food and water is sterilized. Such animals are normally reared in a sterile or microbially-controlled laboratory environment, and they are only exposed to those microorganisms that the researchers wish to have present in the animal. These gnotobionts are used to study the symbiotic relationships between an animal and one or more of the microorganisms that may inhabit its body. This technique is important for microbiologists because it allows them to study only a select few symbiotic interactions at a time (see Scientific control), whereas animals that develop under normal conditions may quickly acquire a microbiota that includes hundreds or thousands of unique organisms.
Such animals may also be used in animal production, especially in the rearing of pigs. After the Caesarean birth, these animals are introduced to their natural microflora in a stepwise fashion. This avoids undesired infections and leads to faster growth.
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