Chapter 2 - Mucosal Microbiota

Abstract

This chapter provides information on the microbial populations on normal mucosal surfaces in humans (the indigenous microbiota). It also evaluates some evidence on how such populations interact with immunologic functions. Microorganisms, principally bacteria, colonize the skin and mucosal surfaces in most areas of the adult human body. Gram-positive, aerobic bacteria predominate on the skin and the mucosa of the nasopharynx and oropharynx. Gram-positive and gram-negative facultative and anaerobic bacteria also colonize the mucosal surface and lumen of major portions of the gastrointestinal (GI) tract. The anaerobic bacteria predominate in both the buccal cavity, the distal one-third of the small intestine, and large intestine. Functional anaerobes also predominate on vaginal surfaces. In aggregate, the microbial populations on all the mucosal surfaces exceed 100 trillion (1*1014) cells. This population, over 99% of which is found in the large intestine, constitutes an indigenous microbiota. This biota establishes on the various mucosal surfaces after birth in patterns that can be recognized as ecologic successions. The indigenous microbiota functions in “colonization resistance” to inhibit the nonindigenous microorganisms and certain indigenous microbial pathogens from proliferating in the mucosal habitats.