Human microbiota - Wikipedia Human microbiota Graphic depicting the human skin microbiota, with relative prevalences of various classes of bacteria The human microbiota is the aggregate of microorganisms that resides on or within any of a number of human tissues and biofluids, including the skin, mammary glands, placenta, seminal fluid, uterus, ovarian follicles, lung, saliva, oral mucosa, conjunctiva, and gastrointestinal tracts. They include bacteria, archaea, protists, fungi and viruses. Though micro-animals also live on the human body, they are typically excluded from this definition. The human microbiome refers specifically to the collective genomes of resident microorganisms. Humans are colonized by many microorganisms ; the traditional estimate is that the average human body is inhabited by ten times as many non-human cells as human cells, but more recent estimates have lowered that ratio to 3 : 1 or even to approximately the same number. Some microbiota that colonize humans are commensal, meaning they co-exist without harming humans ; others have a mutualistic relationship with their human hosts. Conversely, some non-pathogenic microbiota can harm human hosts via the metabolites they produce, like trimethylamine. Certain microbiota perform tasks that are known to be useful to the human host ; the role of most resident microorganisms is not well understood. Those that are expected to be present, and that under normal circumstances do not cause disease, are sometimes deemed normal flora or normal microbiota. The Human Microbiome Project took on the project of sequencing the genome of the human microbiota, focusing particularly on the microbiota that normally inhabit the skin, mouth, nose, digestive tract, and vagina. It reached a milestone in 2012 when it published its initial results. Contents 1 Terminology 2 Relative numbers 3 Study 4 Types 4.1 Bacteria 4.2 Archaea 4.3 Fungi 4.4 Viruses 5 Anatomical areas 5.1 Skin 5.2 Conjunctiva 5.3 Gut 5.4 Vagina 5.5 Placenta 5.6 Uterus 5.7 Oral cavity 5.8 Lung 6 Disease 6.1 Cancer 6.2 Inflammatory bowel disease 6.3 Human immunodeficiency virus 7 Research 8 Environmental health 9 See also 10 Bibliography 11 References 12 External links Terminology Life timeline view discuss edit - 4500 -- -- - 4000 -- -- - 3500 -- -- - 3000 -- -- - 2500 -- -- - 2000 -- -- - 1500 -- -- - 1000 -- -- - 500 -- -- 0 -- water Single - celled life photosynthesis Eukaryotes Multicellular life Land life Dinosaurs Mammals Flowers ← Earliest Earth ( − 4540 ) ← Earliest water ← Earliest life ← LHB meteorites ← Earliest oxygen ← Atmospheric oxygen ← Oxygen crisis ← Earliest sexual reproduction ← Ediacara biota ← Cambrian explosion ← Earliest humans h n r o z o i r o r o z o i r h n d n Pongola Huronian Cryogenian Andean Karoo Quaternary Axis scale : millions of years. Orange labels : known ice ages. Also see : Human timeline and Nature timeline Though widely known as flora or microflora, this is a misnomer in technical terms, since the word root flora pertains to plants, and biota refers to the total collection of organisms in a particular ecosystem. Recently, the more appropriate term microbiota is applied, though its use has not eclipsed the entrenched use and recognition of flora with regard to bacteria and other microorganisms. Both terms are being used in different literature. Relative numbers As of 2014, it was often reported in popular media and in the scientific literature that there are about 10 times as many microbial cells in the human body as there are human cells ; this figure was based on estimates that the human microbiome includes around 100 trillion bacterial cells and that an adult human typically has around 10 trillion human cells. In 2014, the American Academy of Microbiology published a FAQ that emphasized that the number of microbial cells and the number of human cells are both estimates, and noted that recent research had arrived at a new estimate of the number of human cells -- approximately 37.2 trillion, meaning that the ratio of microbial - to - human cells, if the original estimate of 100 trillion bacterial cells is correct, is closer to 3 : 1. In 2016, another group published a new estimate of the ratio being roughly 1 : 1 ( 1.3 : 1, with `` an uncertainty of 25 % and a variation of 53 % over the population of standard 70 - kg males '' ). Study Main article : Human Microbiome Project Flowchart illustrating how the human microbiome is studied on the DNA level. The problem of elucidating the human microbiome is essentially identifying the members of a microbial community which includes bacteria, eukaryotes, and viruses. This is done primarily using DNA - based studies, though RNA, protein and metabolite based studies are also performed. DNA - based microbiome studies typically can be categorized as either targeted amplicon studies or more recently shotgun metagenomic studies. The former focuses on specific known marker genes and is primarily informative taxonomically, while the latter is an entire metagenomic approach which can also be used to study the functional potential of the community. One of the challenges that is present in human microbiome studies but not in other metagenomic studies is to avoid including the host DNA in the study. Aside from simply elucidating the composition of the human microbiome, one of the major questions involving the human microbiome is whether there is a `` core '', that is, whether there is a subset of the community that is shared among most humans. If there is a core, then it would be possible to associate certain community compositions with disease states, which is one of the goals of the Human Microbiome Project. It is known that the human microbiome is highly variable both within a single subject and between different individuals. For example, the gut microbiota of humans is markedly dissimilar between individuals, a phenomenon which is also observed in mice. On 13 June 2012, a major milestone of the Human Microbiome Project ( HMP ) was announced by the NIH director Francis Collins. The announcement was accompanied with a series of coordinated articles published in Nature and several journals in the Public Library of Science ( PLoS ) on the same day. By mapping the normal microbial make - up of healthy humans using genome sequencing techniques, the researchers of the HMP have created a reference database and the boundaries of normal microbial variation in humans. From 242 healthy U.S. volunteers, more than 5,000 samples were collected from tissues from 15 ( men ) to 18 ( women ) body sites such as mouth, nose, skin, lower intestine ( stool ), and vagina. All the DNA, human and microbial, were analyzed with DNA sequencing machines. The microbial genome data were extracted by identifying the bacterial specific ribosomal RNA, 16S rRNA. The researchers calculated that more than 10,000 microbial species occupy the human ecosystem and they have identified 81 -- 99 % of the genera. Types Bacteria Populations of microbes ( such as bacteria and yeasts ) inhabit the skin and mucosal surfaces in various parts of the body. Their role forms part of normal, healthy human physiology, however if microbe numbers grow beyond their typical ranges ( often due to a compromised immune system ) or if microbes populate ( such as through poor hygiene or injury ) areas of the body normally not colonized or sterile ( such as the blood, or the lower respiratory tract, or the abdominal cavity ), disease can result ( causing, respectively, bacteremia / sepsis, pneumonia, and peritonitis ). The Human Microbiome Project found that individuals host thousands of bacterial types, different body sites having their own distinctive communities. Skin and vaginal sites showed smaller diversity than the mouth and gut, these showing the greatest richness. The bacterial makeup for a given site on a body varies from person to person, not only in type, but also in abundance. Bacteria of the same species found throughout the mouth are of multiple subtypes, preferring to inhabit distinctly different locations in the mouth. Even the enterotypes in the human gut, previously thought to be well understood, are from a broad spectrum of communities with blurred taxon boundaries. It is estimated that 500 to 1,000 species of bacteria live in the human gut but belong to just a few phyla : Firmicutes and Bacteroidetes dominate but there are also Proteobacteria, Verrumicrobia, Actinobacteria, Fusobacteria and Cyanobacteria. A number of types of bacteria, such as Actinomyces viscosus and A. naeslundii, live in the mouth, where they are part of a sticky substance called plaque. If this is not removed by brushing, it hardens into calculus ( also called tartar ). The same bacteria also secrete acids that dissolve tooth enamel, causing tooth decay. The vaginal microflora consist mostly of various lactobacillus species. It was long thought that the most common of these species was Lactobacillus acidophilus, but it has later been shown that L. iners is in fact most common, followed by L. crispatus. Other lactobacilli found in the vagina are L. jensenii, L. delbruekii and L. gasseri. Disturbance of the vaginal flora can lead to infections such as bacterial vaginosis or candidiasis ( `` yeast infection '' ). Archaea Archaea are present in the human gut, but, in contrast to the enormous variety of bacteria in this organ, the numbers of archaeal species are much more limited. The dominant group are the methanogens, particularly Methanobrevibacter smithii and Methanosphaera stadtmanae. However, colonization by methanogens is variable, and only about 50 % of humans have easily detectable populations of these organisms. As of 2007, no clear examples of archaeal pathogens were known, although a relationship has been proposed between the presence of some methanogens and human periodontal disease. Fungi See also : Mycobiome Fungi, in particular yeasts, are present in the human gut. The best - studied of these are Candida species due to their ability to become pathogenic in immunocompromised and even in healthy hosts. Yeasts are also present on the skin, such as Malassezia species, where they consume oils secreted from the sebaceous glands. Viruses See also : Human virome Viruses, especially bacterial viruses ( bacteriophages ), colonize various body sites. These colonized sites include the skin, gut, lungs, and oral cavity. Virus communities have been associated with some diseases, and do not simply reflect the bacterial communities. Anatomical areas Main article : List of human flora Skin Main article : Skin flora A study of twenty skin sites on each of ten healthy humans found 205 identified genera in nineteen bacterial phyla, with most sequences assigned to four phyla : Actinobacteria ( 51.8 % ), Firmicutes ( 24.4 % ), Proteobacteria ( 16.5 % ), and Bacteroidetes ( 6.3 % ). A large number of fungal genera are present on healthy human skin, with some variability by region of the body ; however, during pathological conditions, certain genera tend to dominate in the affected region. For example, Malassezia is dominant in atopic dermatitis and Acremonium is dominant on dandruff - afflicted scalps. The skin acts as a barrier to deter the invasion of pathogenic microbes. The human skin contains microbes that reside either in or on the skin and can be residential or transient. Resident microorganism types vary in relation to skin type on the human body. A majority of microbes reside on superficial cells on the skin or prefer to associate with glands. These glands such as oil or sweat glands provide the microbes with water, amino acids, and fatty acids. In addition, resident bacteria that associated with oil glands are often Gram - positive and can be pathogenic. Conjunctiva A small number of bacteria and fungi are normally present in the conjunctiva. Classes of bacteria include Gram - positive cocci ( e.g., Staphylococcus and Streptococcus ) and Gram - negative rods and cocci ( e.g., Haemophilus and Neisseria ) are present. Fungal genera include Candida, Aspergillus, and Penicillium. The lachrymal glands continuously secrete, keeping the conjunctiva moist, while intermittent blinking lubricates the conjunctiva and washes away foreign material. Tears contain bactericides such as lysozyme, so that microorganisms have difficulty in surviving the lysozyme and settling on the epithelial surfaces. Gut Tryptophan metabolism by human gastrointestinal microbiota ( v t e ) This diagram shows the biosynthesis of bioactive compounds ( indole and certain derivatives ) from tryptophan by bacteria in the gut. Indole is produced from tryptophan by bacteria that express tryptophanase. Clostridium sporogenes metabolizes indole into 3 - indolepropionic acid ( IPA ), a highly potent neuroprotective antioxidant that scavenges hydroxyl radicals. In the intestine, IPA binds to pregnane X receptors ( PXR ) in intestinal cells, thereby facilitating mucosal homeostasis and barrier function. Following absorption from the intestine and distribution to the brain, IPA confers a neuroprotective effect against cerebral ischemia and Alzheimer 's disease. Lactobacillus species metabolize tryptophan into indole - 3 - aldehyde ( I3A ) which acts on the aryl hydrocarbon receptor ( AhR ) in intestinal immune cells, in turn increasing interleukin - 22 ( IL - 22 ) production. Indole itself acts as a glucagon - like peptide - 1 ( GLP - 1 ) secretagogue in intestinal L cells and as a ligand for AhR. Indole can also be metabolized by the liver into indoxyl sulfate, a compound that is toxic in high concentrations and associated with vascular disease and renal dysfunction. AST - 120 ( activated charcoal ), an intestinal sorbent that is taken by mouth, adsorbs indole, in turn decreasing the concentration of indoxyl sulfate in blood plasma. Main article : Gut flora See also : Gut -- brain axis The gut flora has the largest numbers of bacteria and the greatest number of species compared to other areas of the body. In humans the gut flora is established at one to two years after birth, and by that time the intestinal epithelium and the intestinal mucosal barrier that it secretes have co-developed in a way that is tolerant to, and even supportive of, the gut flora and that also provides a barrier to pathogenic organisms. The relationship between some gut flora and humans is not merely commensal ( a non-harmful coexistence ), but rather a mutualistic relationship. Some human gut microorganisms benefit the host by fermentating dietary fiber into short - chain fatty acids ( SCFAs ), such as acetic acid and butyric acid, which are then absorbed by the host. Intestinal bacteria also play a role in synthesizing vitamin B and vitamin K as well as metabolizing bile acids, sterols, and xenobiotics. The systemic importance of the SCFAs and other compounds they produce are like hormones and the gut flora itself appears to function like an endocrine organ, and dysregulation of the gut flora has been correlated with a host of inflammatory and autoimmune conditions. The composition of human gut flora changes over time, when the diet changes, and as overall health changes. A systematic review of 15 human randomized controlled trials from July 2016 found that certain commercially available strains of probiotic bacteria from the Bifidobacterium and Lactobacillus genera ( B. longum, B. breve, B. infantis, L. helveticus, L. rhamnosus, L. plantarum, and L. casei ), when taken by mouth in daily doses of 10 -- 10 colony forming units ( CFU ) for 1 -- 2 months, possess treatment efficacy ( i.e., improved behavioral outcomes ) in certain central nervous system disorders -- including anxiety, depression, autism spectrum disorder, and obsessive -- compulsive disorder -- and improved certain aspects of memory. Vagina Main article : Vaginal flora See also : List of microbiota species of the lower reproductive tract of women, List of bacterial vaginosis microbiota, and Vaginal microbiota in pregnancy Vaginal microbiota refers to those species and genera that colonize the lower reproductive tract of women. These organisms play an important role in protecting against infections and maintaining vaginal health. The most abundant vaginal microorganisms found in premenopausal women are from the genus Lactobacillus, which suppress pathogens by producing hydrogen peroxide and lactic acid. Bacterial species composition and ratios vary depending on the stage of the menstrual cycle. Ethnicity also influences vaginal flora. The occurrence of hydrogen peroxide - producing lactobacilli is lower in African American women and vaginal pH is higher. Other influential factors such as sexual intercourse and antibiotics have been linked to the loss of lactobacilli. Moreover, studies have found that sexual intercourse with a condom does appear to change lactobacilli levels, and does increase the level of Escherichia coli within the vaginal flora. Changes in the normal, healthy vaginal microbiota is an indication of infections, such as candidiasis or bacterial vaginosis. Candida albicans inhibits the growth of Lactobacillus species, while Lactobacillus species which produce hydrogen peroxide inhibit the growth and virulence of Candida albicans in both the vagina and the gut. Fungal genera that have been detected in the vagina include Candida, Pichia, Eurotium, Alternaria, Rhodotorula, and Cladosporium, among others. Placenta Main article : Placental microbiome Until recently the placenta was considered to be a sterile organ but commensal, nonpathogenic bacterial species and genera have been identified that reside in the placental tissue. Uterus Main article : Uterine microbiome Until recently, the upper reproductive tract of women was considered to be a sterile environment. A variety of microorganisms inhabit the uterus of healthy, asymptomatic women of reproductive age. The microbiome of the uterus differs significantly from that of the vagina and gastrointestinal tract. Oral cavity Main article : Oral microbiology The environment present in the human mouth allows the growth of characteristic microorganisms found there. It provides a source of water and nutrients, as well as a moderate temperature. Resident microbes of the mouth adhere to the teeth and gums to resist mechanical flushing from the mouth to stomach where acid - sensitive microbes are destroyed by hydrochloric acid. Anaerobic bacteria in the oral cavity include : Actinomyces, Arachnia, Bacteroides, Bifidobacterium, Eubacterium, Fusobacterium, Lactobacillus, Leptotrichia, Peptococcus, Peptostreptococcus, Propionibacterium, Selenomonas, Treponema, and Veillonella. Genera of fungi that are frequently found in the mouth include Candida, Cladosporium, Aspergillus, Fusarium, Glomus, Alternaria, Penicillium, and Cryptococcus, among others. Bacteria accumulate on both the hard and soft oral tissues in biofilms. Bacterial adhesion is particularly important for oral bacteria. Oral bacteria have evolved mechanisms to sense their environment and evade or modify the host. Bacteria occupy the ecological niche provided by both the tooth surface and gingival epithelium. However, a highly efficient innate host defense system constantly monitors the bacterial colonization and prevents bacterial invasion of local tissues. A dynamic equilibrium exists between dental plaque bacteria and the innate host defense system. Of particular interest is the role of oral microorganisms in the two major dental diseases : dental caries and periodontal disease. Additionally, research has correlated poor oral heath and the resulting ability of the oral microbiota to invade the body to affect cardiac health as well as cognitive function. Lung Main article : Lung microbiome Much like the oral cavity, the upper and lower respiratory system possess mechanical deterrents to remove microbes. Goblet cells produce mucous which traps microbes and moves them out of the respiratory system via continuously moving ciliated epithelial cells. In addition, a bactericidal effect is generated by nasal mucus which contains the enzyme lysozyme. The upper and lower respiratory tract appears to have its own set of microbiota. Pulmonary bacterial microbiota belong to 9 major bacterial genera : Prevotella, Sphingomonas, Pseudomonas, Acinetobacter, Fusobacterium, Megasphaera, Veillonella, Staphylococcus, and Streptococcus. Some of the bacteria considered `` normal biota '' in the respiratory tract can cause serious disease especially in immunocompromised individuals ; these include Streptococcus pyogenes, Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, and Staphylococcus aureus. Fungal genera that compose the pulmonary mycobiome include Candida, Malassezia, Neosartorya, Saccharomyces, and Aspergillus, among others. Unusual distributions of bacterial and fungal genera in the respiratory tract is observed in people with cystic fibrosis. Their bacterial flora often contains antibiotic - resistant and slow - growing bacteria, and the frequency of these pathogens changes in relation to age. Disease A symbiotic relationship between the gut microbiota and different bacteria may influence an individual 's immune response. Cancer Although cancer is generally a disease of host genetics and environmental factors, microorganisms are implicated in some 20 % of human cancers. Particularly for potential factors in colon cancer, bacterial density is one million times higher than in the small intestine, and approximately 12-fold more cancers occur in the colon compared to the small intestine, possibly establishing a pathogenic role for microbiota in colon and rectal cancers. Microbial density may be used as a prognostic tool in assessment of colorectal cancers. The microbiota may affect carcinogenesis in three broad ways : ( i ) altering the balance of tumor cell proliferation and death, ( ii ) regulating immune system function, and ( iii ) influencing metabolism of host - produced factors, foods and pharmaceuticals. Tumors arising at boundary surfaces, such as the skin, oropharynx and respiratory, digestive and urogenital tracts, harbor a microbiota. Substantial microbe presence at a tumor site does not establish association or causal links. Instead, microbes may find tumor oxygen tension or nutrient profile supportive. Decreased populations of specific microbes or induced oxidative stress may also increase risks. Of the around 10 microbes on earth, ten are designated by the International Agency for Research on Cancer as human carcinogens. Microbes may secrete proteins or other factors directly drive cell proliferation in the host, or may up - or down - regulate the host immune system including driving acute or chronic inflammation in ways that contribute to carcinogenesis. Concerning the relationship of immune function and development of inflammation, mucosal surface barriers are subject to environmental risks and must rapidly repair to maintain homeostasis. Compromised host or microbiota resiliency also reduce resistance to malignancy, possibly inducing inflammation and cancer. Once barriers are breached, microbes can elicit proinflammatory or immunosuppressive programs through various pathways. For example, cancer - associated microbes appear to activate NF - κΒ signaling within the tumor microenviroment. Other pattern recognition receptors, such as nucleotide - binding oligomerization domain -- like receptor ( NLR ) family members NOD - 2, NLRP3, NLRP6 and NLRP12, may play a role in mediating colorectal cancer. Likewise Helicobacter pylori appears to increase the risk of gastric cancer, due to its driving a chronic inflammatory response in the stomach. Inflammatory bowel disease Inflammatory bowel disease consists of two different diseases : ulcerative colitis and Crohn 's disease and both of these diseases present with disruptions in the gut microbiota ( also known as dysbiosis ). This dysbiosis presents itself in the form of decreased microbial diversity in the gut, and is correlated to defects in host genes that changes the innate immune response in individuals. Human Immunodeficiency virus The HIV disease progression influences the composition and function of the gut microbiota, with notable differences between HIV - negative, HIV - positive, and post-ART HIV - positive populations. HIV decreases the integrity of the gut epithelial barrier function by affecting tight junctions. This breakdown allows for translocation across the gut epithelium, which is thought to contribute to increases in inflammation seen in people with HIV. Vaginal microbiota plays a role in the infectivity of HIV, with an increased risk of infection and transmission when the woman has bacterial vaginosis, a condition characterized by an abnormal balance of vaginal bacteria. The enhanced infectivity is seen with the increase in pro-inflammatory cytokines and CCR5 + CD4+ cells in the vagina. However, a decrease in infectivity is seen with increased levels of vaginal Lactobacillus, which promotes an anti-inflammatory condition. Research Diabetic foot ulcers develop their own, distinctive microbiota. Periodontal disease and urinary tract infections are often linked to bacteria, such as Helicobacter pylori and Chlamydia pneumonia ), numerous viral agents ( Cytomegalo - virus, herpes simplex virus type - 2, HIV ), and parasites ( Plasmodium spp. and Toxoplasma gondii ). 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Digestive system - related fungal infections may be induced by both commensal opportunistic fungi and exogenous pathogenic fungi... Candida sp. is also the most frequently identified species among patients with gastric IFI... It was once believed that gastric acid could kill microbes entering the stomach and that the unique ecological environment of the stomach was not suitable for microbial colonisation or infection. However, several studies using culture - independent methods confirmed that large numbers of acid - resistant bacteria belonging to eight phyla and up to 120 species exist in the stomach, such as Streptococcus sp., Neisseria sp. and Lactobacillus sp. etc. Furthermore, Candida albicans can grow well in highly acidic environments, and some genotypes may increase the severity of gastric mucosal lesions. ^ Jump up to : Erdogan A, Rao SS ( April 2015 ). `` Small intestinal fungal overgrowth ''. Curr Gastroenterol Rep. 17 ( 4 ) : 16. PMID 25786900. doi : 10.1007 / s11894 - 015 - 0436 - 2. Small intestinal fungal overgrowth ( SIFO ) is characterized by the presence of excessive number of fungal organisms in the small intestine associated with gastrointestinal ( GI ) symptoms. Candidiasis is known to cause GI symptoms particularly in immunocompromised patients or those receiving steroids or antibiotics. However, only recently, there is emerging literature that an overgrowth of fungus in the small intestine of non-immunocompromised subjects may cause unexplained GI symptoms. Two recent studies showed that 26 % ( 24 / 94 ) and 25.3 % ( 38 / 150 ) of a series of patients with unexplained GI symptoms had SIFO. The most common symptoms observed in these patients were belching, bloating, indigestion, nausea, diarrhea, and gas... Fungal - bacterial interaction may act in different ways and may either be synergistic or antagonistic or symbiotic ( 29 ). 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External links The Secret World Inside You Exhibit 2015 - 2016, American Museum of Natural History FAQ : Human Microbiome, January 2014 American Society For Microbiology Human microbiota Human flora Gut Lung Mouth Skin Vagina In pregnancy In bacterial vaginosis Placenta Uterus Salivary Human virome Disorders and therapies Dysbiosis Faecal transfer Related : Human Microbiome Project OpenBiome Microbiology : Bacteria Medical microbiology infection Coley 's toxins Exotoxin Lysogenic cycle Pathogenic bacteria resistance Biochemistry and ecology Oxygen preference Aerobic Obligate Anaerobic Facultative Obligate Microaerophile Nanaerobe Aerotolerant Other Microbial metabolism Primary nutritional groups Nitrogen fixation Microbial ecology Human flora Gut Lung Mouth Skin Vaginal ( In pregnancy ) Placental Uterine Salivary Substrate preference Lipophilic Saccharophilic Shape Bacterial cellular morphologies L - form bacteria Coccus Diplococcus Bacillus Coccobacillus Spiral Structure Cell envelope Cell membrane Cell wall : Peptidoglycan NAM NAG DAP Gram - positive bacteria only : Teichoic acid Lipoteichoic acid Endospore Gram - negative bacteria only : Bacterial outer membrane Porin Lipopolysaccharide Periplasmic space Mycobacteria only : Arabinogalactan Mycolic acid Outside envelope Bacterial capsule Slime layer S - layer Glycocalyx Pilus Fimbria Non-motile bacteria Composite Biofilm Taxonomy Bacteria ( classifications ) Bacterial phyla Former groupings : Schizomycetes Monera Prokaryota Gracilicutes Firmicutes Mollicutes Mendosicutes Biology portal Medicine portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Human_microbiota&oldid=799701569 '' Categories : Bacteriology Bacteria and humans Microbiology Microbiomes Environmental microbiology Gut flora Human genome projects Hidden categories : CS1 maint : Explicit use of et al. 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Question: where is the most bacteria found in the human body
Answer: gut flora