Escherichia coli, one of the many species of bacteria present in the human<unk> <unk>  are the microorganisms, including bacteria and archaea, that live in the digestive tracts of vertebrates including humans, and of insects. Alternative terms include<unk>  flora (an outdated term that technically refers to plants) and<unk>  microbiome. The gastrointestinal metagenome (sometimes defined as the microbiome) is the aggregate of all the genomes of<unk> . In the human, the<unk>  is the main location of human microbiota. The<unk>  has broad impacts, including effects on colonization, resistance to pathogens, maintaining the intestinal epithelium, metabolizing dietary and pharmaceutical compounds, controlling immune function, and even behavior through the<unk> -brain axis. The microbial composition of the<unk>  varies across regions of the digestive tract. The colon contains the highest microbial density recorded in any habitat on Earth, representing between 300 and 1000 different species. However, 99% of<unk>  bacteria come from about 30 or 40 species. Bacteria also make up to 60% of the dry mass of feces. Over 99% of the bacteria in the<unk>  are anaerobes, but in the cecum, aerobic bacteria reach high densities. It is estimated that the human<unk>  have around a hundred times as many genes as there are in the human genome.
Gut microbiota
Human microbiome
Human milk microbiome
Vaginal flora
Salivary microbiome
Skin flora
Gastrointestinal physiology
Microbiota-accessible carbohydrates