 Despite the staggering number of microbes in and on the human body, little was known about their roles in human health and disease.Many of the organisms that make up the microbiome have not been successfully cultured, identified, or otherwise characterized.Organisms thought to be found in the human microbiome, however, may generally be categorized as bacteria, members of domain Archaea, yeasts, and single-celled eukaryotes as well as various helminth parasites and viruses, the latter including viruses that infect the cellular microbiome organisms (e.g., bacteriophages).