There are new, very sensitive methods for detecting bacteria. These methods show that hundreds of millions of microbes (organisms that can only be seen with microscopes), especially bacteria, live in healthy people. The collection of different microbes found in a site is called a "microbiome." The investigators know that microbiomes of the skin, sinuses, mouth, gastro-intestinal tract, etc. differ from each other. The make-up of the microbiome - which bacteria are found in a site - may be necessary for good health. For example, the microbiome of the mouth is different in people with inflammation of the gums (periodontitis), and the microbiome of the bowel is different in people with inflammation of the intestinal tract (inflammatory bowel disease).