Human gastrointestinal microbiota

gut floragut microbiotaintestinal floragut bacteriaenteric bacteriagut microbiomeintestinal microbiotaintestinal bacteriagut microfloraintestinal microflora
Human gastrointestinal microbiota, also known as gut flora or gut microbiota, are the microorganisms that live in the digestive tracts of humans.wikipedia
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Bacteria

bacteriumbacterialEubacteria
Intestinal bacteria also play a role in synthesizing vitamin B and vitamin K as well as metabolizing bile acids, sterols, and xenobiotics.
The largest number exist in the gut flora, and a large number on the skin.

Microorganism

microorganismsmicrobemicrobes
Human gastrointestinal microbiota, also known as gut flora or gut microbiota, are the microorganisms that live in the digestive tracts of humans.
In the human body microorganisms make up the human microbiota including the essential gut flora.

Vitamin K

KMenaquinoneVitamin K 1
Intestinal bacteria also play a role in synthesizing vitamin B and vitamin K as well as metabolizing bile acids, sterols, and xenobiotics. Though people can survive with no gut flora, the microorganisms perform a host of useful functions, such as fermenting unused energy substrates, training the immune system via end products of metabolism like propionate and acetate, preventing growth of harmful species, regulating the development of the gut, producing vitamins for the host (such as biotin and vitamin K), and producing hormones to direct the host to store fats.
Bacteria in the gut flora can also convert K 1 into vitamin K 2 (menaquinone).

Large intestine

coloncolorectallarge bowel
The colon, in contrast, contains the highest microbial density recorded in any habitat on Earth with up to 10 12 cells per gram of intestinal content.
It extracts water and salt from solid wastes before they are eliminated from the body and is the site in which flora-aided (largely bacterial) fermentation of unabsorbed material occurs.

Feces

faecesdungexcrement
As a consequence of their abundance in the intestine, bacteria also make up to 60% of the dry mass of feces.
Gut flora produces compounds such as indole, skatole, and thiols (sulfur-containing compounds), as well as the inorganic gas hydrogen sulfide.

Ruminococcus

Ruminococcus productus
Most bacteria belong to the genera Bacteroides, Clostridium, Faecalibacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus, and Bifidobacterium.
They are anaerobic, Gram-positive gut microbes.

Bacteroides

Bacteroides vulgatusB. vulgatusbacteroid
Most bacteria belong to the genera Bacteroides, Clostridium, Faecalibacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus, and Bifidobacterium.
Bacteroides species are normally mutualistic, making up the most substantial portion of the mammalian gastrointestinal microbiota, where they play a fundamental role in processing of complex molecules to simpler ones in the host intestine.

Candida (fungus)

CandidaCandida rugosaTorulopsis
Fungal genera that have been detected in the gut include Candida, Saccharomyces, Aspergillus, Penicillium, Rhodotorula, Trametes, Pleospora, Sclerotinia, Bullera, and Galactomyces, among others.
Many species are found in gut flora, including ''C.

Peptococcus

Peptococci
Most bacteria belong to the genera Bacteroides, Clostridium, Faecalibacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus, and Bifidobacterium.
Species in the genus are part of the human microbiome, especially in the bacteria that form the gut flora.

Peptostreptococcus

Peptostreptococcus microsanaerobic streptococciPeptostreptococci
Most bacteria belong to the genera Bacteroides, Clostridium, Faecalibacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus, and Bifidobacterium.
Peptostreptococcus species are commensal organisms in humans, living predominantly in the mouth, skin, gastrointestinal, vagina and urinary tracts, and are members of the gut microbiota.

Small intestine

small bowelsmall intestinessmall
In the stomach and small intestine, relatively few species of bacteria are generally present.
The presence of gut flora appears to contribute positively to the host's immune system.

Inflammatory bowel disease

inflammatory bowel diseasesIBDindeterminate colitis
Rhodotorula is most frequently found in individuals with inflammatory bowel disease while Candida is most frequently found in individuals with hepatitis B cirrhosis and chronic hepatitis B.
As a result of microbial symbiosis and immunity, alterations in the gut microbiome may contribute to inflammatory gut diseases.

Faecalibacterium

Faecalibacterium prausnitziiFusobacterium prausnitzii
Most bacteria belong to the genera Bacteroides, Clostridium, Faecalibacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus, and Bifidobacterium.
Its sole known species, Faecalibacterium prausnitzii is gram-positive, mesophilic, rod-shaped, anaerobic and is one of the most abundant and important commensal bacteria of the human gut microbiota.

Helicobacter pylori

H. pyloriantibiotic-resistant ''H. pyloribacteria
Helicobacter pylori is a gram-negative spiral bacterium that establishes on gastric mucosa causing chronic gastritis and peptic ulcer disease and is a carcinogen for gastric cancer.
It contains a hydrogenase that can produce energy by oxidizing molecular hydrogen (H 2 ) made by intestinal bacteria.

Enterotype

An enterotype is a classification of living organisms based on its bacteriological ecosystem in the human gut microbiome not dictated by age, gender, body weight, or national divisions. Gut microflora is mainly composed of three enterotypes: Prevotella, Bacteroides, and Ruminococcus.
An enterotype is a classification of living organisms based on its bacteriological ecosystem in the gut microbiome.

Escherichia coli

E. coliE.coliE-coli
Also, there is a decrease in the diversity of the microbiome with low levels of fecal Lactobacilli and Bifidobacteria, high levels of facultative anaerobic bacteria such as Escherichia coli, and increased ratios of Firmicutes: Bacteroidetes.
E. coli and other facultative anaerobes constitute about 0.1% of gut microbiota, and fecal–oral transmission is the major route through which pathogenic strains of the bacterium cause disease.

Butyric acid

butanoate metabolismbutyricbutanoic acid
Some human gut microorganisms benefit the host by fermenting dietary fiber into short-chain fatty acids (SCFAs), such as acetic acid and butyric acid, which are then absorbed by the host.
Highly-fermentable fiber residues, such as those from resistant starch, oat bran, pectin, and guar are transformed by colonic bacteria into short-chain fatty acids (SCFA) including butyrate, producing more SCFA than less fermentable fibers such as celluloses.

Prevotella

Prevotella copriPrevotella nigrescensPrevotella species
Gut microflora is mainly composed of three enterotypes: Prevotella, Bacteroides, and Ruminococcus.
are members of the oral, vaginal, and gut microbiota and are often recovered from anaerobic infections of the respiratory tract.

Methanobrevibacter smithii

ArchaeaM. smithiismithii
Archaea constitute another large class of gut flora which are important in the metabolism of the bacterial products of fermentation.
The human gut flora consists of three main groups of hydrogen-consuming microorganisms or hydrogenotrophs: methanogens including ''M.

Disease

morbidityillnessdiseases
However, in certain conditions, some species are thought to be capable of causing disease by causing infection or increasing cancer risk for the host.

Clostridium perfringens

C. perfringensClostridium welchiiCl. welchii
C. perfringens is ever-present in nature and can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates, insects, and soil.

Immune system

immuneimmune responseimmune function
Though people can survive with no gut flora, the microorganisms perform a host of useful functions, such as fermenting unused energy substrates, training the immune system via end products of metabolism like propionate and acetate, preventing growth of harmful species, regulating the development of the gut, producing vitamins for the host (such as biotin and vitamin K), and producing hormones to direct the host to store fats.
Within the genitourinary and gastrointestinal tracts, commensal flora serve as biological barriers by competing with pathogenic bacteria for food and space and, in some cases, by changing the conditions in their environment, such as pH or available iron.

Commensalism

commensalcommensalscommensally
The relationship between some gut flora and humans is not merely commensal (a non-harmful coexistence), but rather a mutualistic relationship.
Whether the relationship between humans and some types of gut flora is commensal or mutualistic is still unanswered.

Escherichia

Other genera, such as Escherichia and Lactobacillus, are present to a lesser extent.
While many Escherichia are commensal members of the gut microbiota, certain strains of some species, most notably the serotypes of Escherichia coli, are human pathogens, and are the most common cause of urinary tract infections, significant sources of gastrointestinal disease, ranging from simple diarrhea to dysentery-like conditions, as well as a wide range of other pathogenic states classifiable in general as colonic escherichiosis.

Gut–brain axis

gut-brain axisbiochemical signaling that takes place between the gastrointestinal tract and the central nervous systembrain-gut
When the gut flora first started to be studied, it was thought to have three key roles: directly defending against pathogens, fortifying host defense by its role in developing and maintaining the intestinal epithelium and inducing antibody production there, and metabolizing otherwise indigestible compounds in food; subsequent work discovered its role in training the developing immune system, and yet further work focused on its role in the gut-brain axis.
The term "gut–brain axis" is occasionally used to refer to the role of the gut flora in the interplay as well, whereas the term "microbiome–gut–brain axis" explicitly includes the role of gut flora in the biochemical signaling events that take place between the GI tract and CNS.