ABSTRACT
It is estimated that humans harbor 1013-1014 microbial cells. These cells mainly grow on the epithelial surface of the body. They present as a complex microbial community. Prevalent area includes skin, mouth, vagina, and gastrointestinal tract. Some of the microorganisms can grow in even acidic environments such as in the stomach where the pH is 2. This complex microbial community is generally called microbiota that consists of thousands of different microbial members. They include bacteria, archaea, fungi, viruses, and eukaryotic microorganisms present in specic epithelial tissues. We focus on the microbiota present in gastrointestinal tracts that inuence the nutrition, metabolism, physiology, and immune function of the host. They participate in breaking down of complex carbohydrates that are present in regular diets and help the host. Similarly, this microbiota has the property to protect the host from pathogenic microbial organisms as well by competing for resources or even inhibiting the growth of the pathogen.
