Intestinal flora

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Accumulation of Escherichia coli (secondary electron microscopy)

The intestinal flora (syn. Intestinal flora , intestinal microbiota , intestinal microbiome ) refers to the entirety of the microorganisms that colonize the intestines of humans and animals (even of insects) and are of crucial importance for the host organism. There is thus an interrelation between living beings of two species . The intestinal flora belongs to the microbiome of a multicellular cell.

The term " flora " is based on the earlier held view that bacteria and many other microorganisms belong to the plant kingdom. Since bacteria now form their own domain , one should correctly speak of an intestinal microorganism community or an intestinal microbiota. These terms are only slowly gaining acceptance in medicine.

composition

Intestinal flora of humans

The human intestine is colonized by bacteria , archaea and eukaryotes . It represents a complex and dynamic bacterial ecosystem that is established within the first years of life. The colonization density of the intestine is initially low and increases steadily with increasing age. During the birth process and shortly afterwards, the first bacterial colonization of the previously sterile human digestive tract occurs . In naturally born children, colonization begins during birth. The first microorganisms that can be detected are Escherichia coli , enterobacteria and streptococci . Children born by caesarean section initially receive an unnatural intestinal flora that corresponds to the maternal skin flora.

Food has a particular influence on settlement. Whether a child is breastfed or is being fed bottle feeding can be seen from the intestinal flora. After the first few weeks, the intestines of breastfed children are mainly populated by lactic acid-producing bacteria ( bifidobacteria and lactobacilli ). The lactic acid they produce leads to acidification of the intestinal environment, which makes it difficult for pathogenic bacteria to settle there. In contrast, an adult-like microflora is detected in bottle- fed children .

The intestinal flora of adults is characterized by a large number of different types of bacteria. In a healthy middle-aged adult, this ecosystem is made up of mostly anaerobic bacteria, totaling 10 to 100 trillion. Molecular analyzes of the 16S ribosomal DNA have so far increased culture-dependent estimates from 200 to 300 species to up to 1,800 genera with up to 36,000 species. The colonization of a human belonging to the intestinal canal contains at least 500 to 1000 different species. The microorganisms colonize the intestinal lumen, the mucin layer and the mucosal surfaces. In contrast to the small intestine with 10 3 to 10 7 (ten million) individuals per gram of feces, the large intestine is densely populated with 10 11 (one hundred billion) to 10 12 (one billion) individuals per gram. The total mass of the microflora in the intestinal tract of an adult person is between 1000 and 2000 grams, with over 50% of the microorganisms observable under the microscope in stool samples cannot be cultivated .

The intestinal flora consists to 99% of four bacterial departments (Phyla = strains): Firmicutes , Bacteroidetes , Proteobacteria and Actinobacteria . In middle-aged people almost exclusively obligate anaerobes ( Bacteroides , Bifidobacterium , Eubacterium , Clostridium , Fusobacterium , Ruminococcus , Roseburia ) are found in the large intestine , while the small intestinal microflora is mainly composed of facultative anaerobic bacteria such as Enterococcus and Lactobacillus arteries. There are different biovars of the species Escherichia coli . Some of these biovars are completely harmless as intestinal inhabitants of humans, but others are pathogenic: enterohaemorrhagic E. coli (EHEC), enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), enterotoxic E. coli (ETEC). Escherichia coli is easy to cultivate and is used as a model organism in microbiology .

Intestinal flora of the dog

The intestinal flora in dogs consists of 99% five bacterial departments. In addition to Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria as in humans, Fusobacteria occur in dogs . In healthy dogs, Helicobacter spp. Is found in the stomach and invasively colonizes the gastric mucosa, including the gastric glands. Clostridia , lactic acid bacteria and Proteobacteria predominate in the small intestine , and Clostridiales , Bacteroides , Prevotella and Fusobacteria in the large intestine . It should be noted that each animal has an individual intestinal microbiome.

Use, function, meaning

There are around 1.3 times as many microorganisms in the intestine as there are cells in the human organism . There are many more microorganisms in the large intestine than in the small intestine. The intestinal microflora is involved in the defense against pathogens ( colonization resistance ) and influences the immune system , although it is not entirely clear whether there is an advantage for the host as a whole. Experiments with normal mice free of microorganisms have shown that various bacteria and amoebas only become pathogenic through the presence of the intestinal flora, while the negative effects of some other eukaryotic unicellular organisms and flukes are reduced. The constancy of the milieu conditions in the intestine and the diversity of the substrates supplied in the form of food favor the development of a microorganism society that is extremely complex in terms of the number of individuals and species and activities. Food components and substances formed by the human organism serve the microorganisms as a source of nutrients and energy. The microorganisms have different effects on humans like

During the microbial breakdown of indigestible carbohydrates (fiber), short-chain fatty acids (mainly acetic, propionic and butyric acid) and gases such as hydrogen (H 2 ), carbon dioxide (CO 2 ) and methane (CH 4 ) are formed in the human intestine . Intestinal epithelial cells take up the fatty acids and metabolize them; the gases are excreted ( flatulence ). Among the short-chain fatty acids, butyric acid is particularly important because of its physiological effects. For example, decreased intestinal butyric acid concentrations have been observed in colon cancer. Another function of the short-chain fatty acids is to stimulate intestinal peristalsis , the contractive movement of the intestine to transport food pulp towards the rectum .

Metabolism of short-chain fatty acids formed by bacteria

During the anaerobic metabolism of proteins, short-chain but also branched- chain fatty acids are formed (iso-valeric acid, iso-butyric acid). In addition, products such as thiols (mercaptans), indoles , amines and hydrogen sulfide (H 2 S) can also be formed. Nitrogen (N 2 ) is also formed to a small extent . Fats are not metabolized in the intestine under anoxic conditions.

The intestinal flora influences the body weight and plays a role in obesity ( obesity ). From experiments on "fat" (English obese ) mutants (ob / ob) who lack the fatty acid regulator leptin , it is known that the intestinal flora of fat and slender mice differ with regard to the composition of the ratio of bacteria of the genus Bacteroides and the strain (Department ) of Firmicutes , whereby fat mice have a larger proportion of Firmicutes. The human intestinal flora also has an influence on body weight. In the intestines of healthy people, Firmicuten and Bacteroideten strains are found in a ratio of 1: 1 to 3: 1. In overweight patients, the ratios in favor of the Firmicutes are often shifted from 3: 1 to up to 25: 1 (in extreme cases up to 200: 1). A dominance of the Firmicutes leads to a better breakdown of fiber and the production of additional energy. Obesity is therefore also a result of an improved energy supply through excessively strong firmicutes. When you lose weight, the ratio of Firmicutes to Bacteroides shifts. The mutual influence of the composition of the intestinal flora and the body weight is associated with the energy intake, because the digestion of fatty acids and polysaccharides is influenced by the composition of the intestinal flora. This is evident from experiments in which the intestinal flora (from the caecum ) of fat mice was transplanted into microorganism-free mice, and these subsequently gained weight, despite a reduction in food intake.

It is discussed to what extent the composition of the intestinal flora in mice, as in humans, has an influence on emotional behavior and the handling of stress.

In their function as commensals , the mere quantity of the microorganisms prevents the overgrowth of pathogenic microorganisms, as happens with Clostridium difficile in pseudomembranous colitis . Conversely, the administration of stool from a healthy donor through an enema (via the rectum or a lying nasoduodenal tube ) can cure therapy-resistant pseudomembranous colitis in the majority of cases, as studies have shown. Successes with other chronic inflammatory bowel diseases have also been reported.

With about 30% of the dry matter, the intestinal flora is an essential part of the faeces .

Incorrect colonization of the intestine

Changes in the intestinal flora can consist of under- or over-population and a change in their composition. Incorrect colonization can occur in either the large or small intestine, or both at the same time. The optimal composition of the intestinal flora depends on the host. Mice which are equipped with a typical intestinal flora from humans or from rats have weak points in their immune system compared with mice which have the typical intestinal flora for mice.

Symptoms

These generally include abdominal pain, gas, an increased susceptibility to infection and susceptibility to food intolerance . If the flora in the small intestine is disturbed, a flat stomach occurs without leaving intestinal gases, and the stomach flattens out again overnight. In the case of an incorrect colonization of the large intestine, on the other hand, the bloated stomach occurs with outgoing intestinal gases. Effects on the immune system and connections between the disturbed colonization of the intestines and the nervous system can also be observed.

diagnosis

In order to check for incorrect colonization, a lactulose H 2 breath test is first carried out to rule out an incorrect colonization in the small intestine . In addition, a detailed H 2 breath test with lactose or fructose is recommended , as these intolerances can be due to bacterial overgrowth. If an incorrect colonization of the small intestine has been excluded, the intestinal flora status can also be determined with the help of a stool sample in order to check for an incorrect colonization of the large intestine.

Research history

Since it was discovered that bacteria can cause disease, the existence of the intestinal flora was mistaken for a disease which was dubbed "intestinal toxemia" after its discovery: Sir Arbuthnot Lane, the surgeon of the British royal family, recommended that his patients seek advice because of the dangerous Having gut dwellers removed the colon. Colon cleansing became fashionable among doctors. In the subsequent episode, the topic was largely ignored by research. The anaerobic microorganisms could not be examined in the laboratory.

It was only with the advent of antibiotics , whose bactericidal properties damaged the intestinal flora, and the consequences of this damage that the topic was put back on the research agenda. Ultimately, due to the practical difficulties, there was initially no great progress. This was due to the fact that only a fraction of the intestinal microbiota could be detected with the classic culture methods. The picture of the composition of the intestinal flora has changed in some cases fundamentally since the introduction of molecular techniques.

Influencing the intestinal flora

First of all, during a vaginal birth, the infant's bowel is colonized immediately. Enterobacteria and streptococci are initially detectable in the stool, and bifidobacteria and ruminococcus species are soon to be predominant in breast milk . There is a connection between maternal vaginal flora and fetal intestinal flora in vaginal births.

Medical interventions

Damage to the intestinal flora by antibiotics is a side effect of this group of drugs and can lead to antibiotic-associated diarrhea . Normally, however, the original equilibrium is restored within a few weeks. Intensive and constant antibiotic treatment can permanently disrupt the colonization of microorganisms in the intestine, especially in children. Every fourth drug from human medicine has a negative effect on intestinal bacteria and can contribute to antibiotic resistance .

To what extent the intestinal flora can be influenced by the addition of microorganisms, for example probiotics (" symbiosis control "), is scientifically controversial.

In the treatment of Clostridium difficile intestinal infections ( antibiotic-associated colitis ) and other bacterial-induced intestinal inflammations, fecal bacteria therapy in the form of stool transplantation has been used with great success for several years . In this process, stool from a healthy donor is dissolved in physiological saline solution, cleaned and either placed in the colon via an enema or in the recipient's stomach via a nasogastric tube.

According to the results of recent research, BLIS is recommended as a possible renovation. In a study, the positive influence on the condition of the intestines is confirmed by the administration of probiotics.

See also

literature

  • Jörg Blech: Life on Humans - The History of Our Settlers. Rowohlt-Verlag, 2010, ISBN 978-3-499-62494-0 .
  • Peter Brookesmith, Karin Prager: Little Monsters. The secret world of tiny living things. Gondrom-Verlag, 1999, ISBN 3-8112-1735-6 , pp. 55-59.
  • J. Müller, R. Ottenjann, J. Seifert (Hrsg.): Gut ecosystem - morphology. Microbiology. Immunology. Springer-Verlag, Berlin 1989, ISBN 3-540-51707-3 .
  • Rosemarie Blatz: Medical Microbiology and Immunology - Systematic. Uni-Med, Bremen 1999, ISBN 3-89599-139-2 .
  • Jürgen Schulze ao: probiotics; Microecology, microbiology, quality, safety and health effects. Hippokrates-Verlag, 2008, ISBN 978-3-8304-5356-7 .
  • BD Muegge, J. Kuczynski: Diet drives convergence in gut microbiome functions across mammalian phylogeny and within humans. In: Science . Volume 332, Number 6032, May 2011, pp. 970-974, ISSN  1095-9203 . doi: 10.1126 / science.1198719 . PMID 21596990 . PMC 3303602 (free full text).

Web links

Wiktionary: Gut flora  - explanations of meanings, word origins, synonyms, translations

Individual evidence

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