A diverse microbial flora is associated with the skin and mucous membrane of every human being from shortly after birth until death. The human body which contains about 1013 cells routinely harbors about 1014 bacteria. This bacterial population constitutes the normal microbial flora. The normal microbial flora is relatively stable with specific genera populating various body regions during particular periods in an individual’s life. Tannock (1995).
Microorganisms of the normal flora may aid the host [By competing for micro-environment more effectively than such pathogens Salmonella Spp or by producing nutrients that the host can use. It may harm the host by causing dental caries, abscesses or other infectious diseases or it may exist as commercials by inhabiting the host for long periods without causing detectable harm or benefits. Even though most elements of the normal microbial flora inhabiting the human skin, nails, eyes, genitalia and gastrointestinal tract are harmless in healthy individuals, these organisms frequently cause disease in compromised hosts.
The normal flora in human usually develops in an orderly sequence, after birth leading to the stable populations of bacteria that made up the normal adult flora. The main factor determining the composition of the normal flora in a body region is the nature of the local environment which is determined by pH, temperature, redox potential, oxygen, water and nutrient levels. Other factors such as peristalsis, saliva hysozyme secretion and secretion of immunoglobulin also play roles in flora control. The local environment is like a concern to in which one principal instrument usually dominates. For example, an infact begins to contact organisms as it moves through the birth canal. A gram positive population [Bifido bacteria] predominates in the gastrointestinal tract early in life. If the infant is breast-fed. This bacterial population is reduced and displaced some what by a gram negative flora [Entero bacteriaceae] when the baby is bottle feel. The type of liquid diet provided to the infant is the principal instrument of this flora controls, immunoglobulins and perhaps other element is breast milk may also be important.