Picture a bustling city on a weekday morning, the sidewalks flooded with people rushing to get to work or to appointments. Now imagine this at a microscopic level and you have an idea of what the microbiome looks like inside our bodies, consisting of trillions of microorganisms (also called microbiota or microbes) of thousands of different species.  These include not only bacteria but fungi, parasites, and viruses. In a healthy person, these “bugs” coexist peacefully, with the largest numbers found in the small and large intestines but also throughout the body. The microbiome is even labeled a supporting organ because it plays so many key roles in promoting the smooth daily operations of the human body.
Each person has an entirely unique network of microbiota that is originally determined by one’s DNA. A person is first exposed to microorganisms as an infant, during delivery in the birth canal and through the mother’s breast milk.  Exactly which microorganisms the infant is exposed to depends solely on the species found in the mother. Later on, environmental exposures and diet can change one’s microbiome to be either beneficial to health or place one at greater risk for disease.
The microbiome consists of microbes that are both helpful and potentially harmful. Most are symbiotic (where both the human body and microbiota benefit) and some, in smaller numbers, are pathogenic (promoting disease). In a healthy body, pathogenic and symbiotic microbiota coexist without problems. But if there is a disturbance in that balance—brought on by infectious illnesses, certain diets, or the prolonged use of antibiotics or other bacteria-destroying medications – dysbiosis occurs, stopping these normal interactions. As a result, the body may become more susceptible to disease.