Normal Flora of Human Body

In a healthy human, the internal tissues, e.g. blood, brain, muscle, etc., are normally free of microorganisms. However, the surface tissues, i.e., skin and mucous membranes, are constantly in contact with environmental organisms and become readily colonized by various microbial species. The mixture of organisms regularly found at any anatomical site is referred to as the normal flora. The normal flora of humans consists of a few eucaryotic fungi and protists, but bacteria are the most numerous and obvious microbial components of the normal flora. A healthy foetus in utero is free from microorganisms. During birth the infant in exposed to vaginal flora. Within a few hours of birth oral and nasopharyngeal flora develops and in a day or two resident flora of the lower intestine appears