Association of germfree mice with human intestinal flora

Microorganisms that inhabit the internal and external surfaces of a healthy host are called the normal or indigenous flora. Human body surfaces that are populated by indigenous flora include the skin, mouth, nose, throat, gastrointestinal tract, vagina and the outer portion of the urethra (Hentges, 1993). Most of the indigenous flora components are anaerobic bacteria.

The relationship between the host and its indigenous flora is usually mutualistic, as components of the flora multiply actively in the host while the host derives benefits from the presence of the flora. However, the relationship becomes a parasitic one when the host defenses are impaired and infections are produced by components of the flora.

Among all the inhabited surfaces of the human body, the gastrointestinal tract contains the largest total population of microorganisms. However, significant variations in the quantitative and qualitative aspects of the flora are observed at different levels of the gastrointestinal tract (Tancrede, 1992).