Harley, John P. Department of Biological Sciences, Eastern Kentucky University, Richmond, Kentucky.
Last reviewed:January 2020
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- Nose and nasopharynx
- Respiratory tract
- External ear
- Small intestine
- Large intestine (colon)
- Genitourinary tract
- Related Primary Literature
- Additional Reading
Microbial flora harbored by normal, healthy persons. The term "human microbiota" pertains to the totality of microorganisms that are present on and in the human body. Although a normal fetus is sterile, the infant is exposed to an increasing number of microorganisms during and after birth. Subsequently, those microorganisms best adapted to survive and colonize particular sites establish themselves and become predominant. Moreover, in a healthy human, internal tissues (such as the brain, blood, cerebrospinal fluid, and muscles) are normally free of microorganisms. Conversely, surface tissues (such as skin and mucous membranes) are constantly in contact with environmental microorganisms and are readily colonized by certain microbial species (Fig. 1). In general, the mixture of microorganisms regularly found at any anatomical site is referred to as the normal microbiota, the indigenous microbial population, the microbiome, the microflora, or the normal flora. For consistency, the term normal microbiota is used here. Because bacteria make up most of the normal microbiota, they are emphasized over the fungi (mainly yeasts) and protozoa. See also: Bacteria; Ecological communities; Fungi; Immune regulation by the microbiome; Medical bacteriology; Microbial ecology; Microbial interactions; Microbiome; Protozoa
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