Human microbiota.

The term human microbiota refers to an ecosystem made up of trillions of microorganisms that inhabit the human body. These microbial communities consist mostly of bacteria but also include viruses, fungi, and other microorganisms. They reside both in and on the body in such diverse locations as the mouth, lungs, skin, genitals, and digestive tract. While attaining an accurate count of human microbiota is difficult, a 2012 study by the National Institutes of Health (NIH) estimated that the body contains thousands of different species of microbes. Many of these microorganisms exist in a symbiotic relationship with humans, helping in the digestion of food and protecting against attacks by other bacteria. Negatively altering the human-microbe ecosystem may lead to certain diseases or medical conditions.