Catad_tema Dysbacteriosis - articles
Yu.O. Shulpekova
Department of Propaedeutics of Internal Diseases, Faculty of Medicine, MMA named after. THEM. Sechenova, Moscow The compositional features and role of intestinal symbiont bacteria in maintaining health are considered. The correctness of using the term “dysbacteriosis” in clinical practice; diseases and conditions that are often mistakenly interpreted as dysbacteriosis are indicated. Given brief overview diseases for which the effectiveness of some probiotics has been confirmed by the results of comparative studies. Indications for the use of the modern combined probiotic drug Linex, its advantages and dosage regimens are presented.
The history of studying the role of intestinal microflora in maintaining human health dates back to the end of the 19th century, when the concept of disease as a consequence of intestinal “autointoxication” developed.
But even today we have to admit that we still know little about the interaction between our body and the bacteria inhabiting it, and it is very difficult to assess the composition of the microflora inhabiting it. gastrointestinal tract(Gastrointestinal tract), from the standpoint of “norm” and “pathology”.
Composition and physiological significance intestinal microflora
More than 400 species of microorganisms live in the human gastrointestinal tract. The content of colony-forming units (CFU) in 1 ml of intraluminal contents increases from 10 2–3 to 10 11–12 as it moves from the stomach to the colon. At the same time, the proportion of anaerobic microorganisms increases and their oxidative potential decreases.
Intestinal bacteria are represented by the main (dominant, or resident), accompanying and residual populations.
The dominant population consists mainly of bacteria from the Lactobacillus, Bifidobacteria and Bacteroides families.
The associated population is represented by Escherichia coli, eubacteria, fusobacteria, enterococci and peptococci.
The residual population includes yeast-like fungi, bacilli, clostridia, Proteus, etc. Some of these microorganisms have more or less pronounced pathogenic properties. It is generally accepted that healthy person No more than 15% of intestinal microbes have pathogenic or opportunistic characteristics.
IN upper sections The gastrointestinal tract microflora composition is similar to that of the oropharynx; a significant proportion of it is represented by streptococci. In the distal direction, the content of lactobacilli gradually increases, and in the large intestine bifidobacteria predominate.
By modern ideas, the main role in maintaining the normal physiological state of the gastrointestinal microflora is played by bacteria of the families Lactobacillus and Bifidobacteria, which are gram-positive, non-spore-forming anaerobes that do not have pathogenic properties. An important characteristic of these microorganisms is the saccharolytic type of metabolism. In the process of fermentation of carbohydrates under the action of enzymes of lactobacilli and bifidobacteria, short-chain fatty acids are formed - lactic, acetic, butyric, propionic. In the presence of these acids, the development of opportunistic strains, which for the most part have a proteolytic type of metabolism, is inhibited. Suppression of proteolytic strains is accompanied by inhibition of putrefactive processes and suppression of the formation of ammonia, aromatic amines, sulfides, and endogenous carcinogens. Thanks to the production of fatty acids, the pH of the intestinal contents is regulated.
Short-chain fatty acids play an important role in regulating metabolism. Entering the systemic bloodstream, they provide up to 20% of the body's daily energy needs, and also serve as the main energy supplier for the epithelium of the intestinal wall.
Butyric and propionic acids increase mitotic activity and regulate epithelial differentiation. Lactic and propionic acids regulate calcium absorption. Their role in the regulation of cholesterol metabolism and glucose metabolism in the liver is of great interest.
Lactobacilli and bifidobacteria synthesize amino acids, proteins, vitamins B1, B2, B6, B12, K, nicotinic and folic acids, substances with antioxidant activity.
Basic population bacteria play an important role in the digestion of milk components. Lactobacilli and enterococcus are capable of breaking down lactose and milk proteins. Phosphoprotein phosphatase secreted by bifidobacteria is involved in the metabolism of casein. All these processes take place in the small intestine.
Lactobacillus species inhabiting the intestines include: L. acidophilus, L. casei, L. bulgaricus, L. plantarum, L. salivarius, L. rhamnosus, L. reuteri. Among bifidobacteria, B. bifidum, B. longum, and B. infantis are distinguished.
Of the aerobic microorganisms belonging to the accompanying population, a serious role in the microbial biocenosis of the intestine belongs to the non-hemolytic Escherichia coli, which produces vitamins (B1, B2, B6, B12, K, nicotinic, folic, pantothenic acids), participates in the metabolism of cholesterol, bilirubin, choline, bile and fatty acids, indirectly affects the absorption of iron and calcium.
As knowledge about the vital functions of intestinal microflora expands, the idea of its important role in maintaining the tension of local and systemic immunity is becoming increasingly clear.
There are protective mechanisms in the intestines that prevent excessive reproduction and introduction of microflora. These include the integrity of the epithelium and the brush border (the distance between the microvilli of which is less than the size of the bacterium), the production of immunoglobulin A, the presence of bile, the presence of Peyer’s patches, etc.
Thanks to the production of substances with antibacterial activity(bacteriocins, short-chain fatty acids, lactoferrin, lysozyme) normal microflora provides local protection against excessive proliferation of opportunistic microorganisms and the introduction of pathogenic microorganisms. The presence of a constant microbial irritant and contact with macrophages and lymphocytes in the area of Peyer's patches provide sufficient tension local immunity, production of immunoglobulin A and high phagocytic activity. At the same time, constant contact with immune cells underlies immunological tolerance.
Components of intestinal bacteria penetrate the systemic bloodstream, thus maintaining the necessary degree of tension of systemic immunity and ensuring its “acquaintance” with the microflora of the environment.
However, even those intestinal bacteria that are considered non-pathogenic and do not have a distinct ability for adhesion, invasion and production of toxins, if local mechanisms defenses are theoretically capable of causing damage to the intestinal wall and possibly also systemic infection. Therefore the purpose medicines based on intestinal bacteria (probiotics) should always be justified.
Causes of disturbances in the composition of intestinal microflora
The composition of the intestinal microbial population, even in a healthy person, is subject to variability and, apparently, reflects the body’s ability to adapt to dietary and lifestyle characteristics and climatic factors.
It must be admitted that general concept“dysbacteriosis,” which until recently was widely used to designate disturbances in the composition of the intestinal microflora, does not fully reflect the essence of such changes and does not allow one to clearly formulate a diagnosis and determine treatment tactics.
Thus, we can distinguish individual diseases and syndromes, which are often mistakenly interpreted as dysbacteriosis:
Each of these diseases has its own cause, certain risk factors, clinical picture, diagnostic criteria and treatment tactics. Of course, against the background of these diseases, secondary disturbances in the microbial composition of the intestine can develop.
Perhaps the most common syndrome in clinical practice is bacterial overgrowth, characterized by a decrease in the number of anaerobes (especially bifidobacteria), an increase total number functionally inferior forms of E. coli (“lactose-”, “mannitol-”, “indole-negative”), content hemolytic forms E. coli and creating conditions for the proliferation of Candida spp.
Bacterial overgrowth syndrome develops against the background of disorders of luminal or parietal digestion (congenital enzyme deficiency, pancreatitis, gluten enteropathy, enteritis), passage of intestinal contents (intestinal fistulas, “blind loops” of the intestine, diverticula, peristalsis disorders, intestinal obstruction); reduction protective properties mucous membrane (anacidic conditions, immunodeficiencies); iatrogenic effects on the intestinal microflora (use of corticosteroids, cytostatics, especially in weakened and elderly patients).
Excessive proliferation of bacteria is observed mainly in the small intestine, since the most favorable nutrient environment is created here. Manifestations of bacterial overgrowth syndrome, such as flatulence, rumbling, abdominal transfusion, loose stool, hypovitaminosis, weight loss, often come to the fore in clinical picture the main diseases listed above.
Tests confirming the presence pathological disorders microflora composition
As in the diagnosis of other diseases, adequate methods must be used to assess changes in the intestinal microflora.
Stool culture for dysbacteriosis, which is common in Russia, cannot be considered an informative test, especially since pathological changes microflora mainly affect the small intestine. This method is valuable in ruling out enteric infections as well as C. difficile infection.
Has very high accuracy microbiological examination culture of an aspirate of the contents of the small intestine.
A breath test with 14C-xylose, hydrogen tests with lactulose and glucose can detect the presence of bacterial overgrowth in the intestines, but do not provide information about the composition of the microflora.
Determination of the spectrum of fatty acids in feces by gas-liquid chromatographic analysis makes it possible to approximately estimate the quantitative ratio various types intestinal bacteria.
Use of probiotics
At the beginning of the 20th century, the great Russian scientist I.I. Mechnikov. put forward the hypothesis that the high content of lactobacilli in the intestinal biocenosis is a necessary condition human health and longevity. Mechnikov I.I. conducted experiments on the use of medicinal purposes live culture of bifidobacteria.
In subsequent years, the development of drugs based on microorganisms with beneficial properties- so-called probiotics.
As a potential therapeutic agent, lactobacilli initially received the most attention as the bacteria with the best studied beneficial properties. Since the 1920s L. acidophilus culture began to be used in the form of acidophilus milk for the treatment of gastrointestinal diseases accompanied by constipation. Since the 1950s Experience is accumulating in the use of L. acidophilus and other cultures to prevent antibiotic-associated diarrhea.
As microbiology developed, new information was obtained about the positive properties of bifidobacteria, E. coli, and non-toxigenic lactic acid streptococcus - Streptococcus (or Enterococcus) faecium. Certain strains of these microorganisms and their combinations began to be included in probiotic preparations.
When studying the ability of microbes to adhere to epithelial cells of the small intestine, it was shown that the use of microorganisms in combination increases their ability to attach to the brush border area.
Mechanisms therapeutic effect probiotics include: suppression of the growth of pathogenic microorganisms, restoration of epithelial integrity, stimulation of the secretion of immunoglobulin A, suppression of the production of pro-inflammatory cytokines, normalization of metabolic processes.
Modern approach to development similar drugs implies, firstly, the use of microorganisms in combinations and, secondly, their release in capsulated form, allowing long-term storage at normal temperature. Clinical experimental studies have shown that under the influence gastric juice and bile, probiotics lose up to 90% of their activity before they enter the intestines. Methods are being developed to increase the survival rate of bacteria - due to their immobilization on porous microcarriers and the inclusion of nutrient medium components in the composition of the drug.
Despite the “theoretically” sound development of probiotic preparations, not all of them turn out to be effective in practice. To date, data from many open and blind controlled studies have been accumulated, the results of which have led to some conclusions about the prospects for the use of certain types of microorganisms for various intestinal diseases.
It has been shown that L. rhamnosus strain GG has the greatest effect in the treatment of infectious gastroenteritis in children, and E. faecium SF68 in adults.
According to some reports, during the recovery period after viral gastroenteritis it is advisable to prescribe drugs containing lactobacilli or their combinations with bifidobacteria and enterococcus; Subspecies of bifidobacteria contribute to the speedy resolution of bacterial intestinal infections.
The ability to reduce the incidence of antibiotic-associated diarrhea has been established for the following bacteria in probiotics:
To reduce frequency side effects For anti-Helicobacter therapy, it is recommended to take simultaneous probiotics containing L. rhamnosus and S. Boulardii, or a combination of L. acidophilus with Bifidobacterium lactis.
A combination of L. acidophilus, L. Bulgaricus and Streptococcus thermophilus was effective in preventing the development of traveler's diarrhea.
According to a meta-analysis, a probiotic containing S. boulardii is most effective in treating recurrent C. Difficile infection (pseudomembranous colitis).
In irritable bowel syndrome, the effect of probiotics on the severity of symptoms such as bloating, pain, and overall symptoms was studied. The effectiveness of microorganisms E. faecium, L. plantarum, as well as the VSL#3 mixture (combination of Bifidobacterium breve, B. longum, B. infantis, L. acidophilus, L. plantarum, L. casei, L. bulgaricus, S. thermophilus) has been demonstrated , mixtures of L. acidophilus, L. plantarum and B. breve and mixtures of L. salivarius and B. infantis. However, these data were obtained on relatively small groups of patients, so they have not yet been reflected in international recommendations for the treatment of patients with irritable bowel syndrome.
There is an urgent question about the possibility of using probiotics for the treatment and prevention of exacerbations in chronic inflammatory bowel diseases - ulcerative colitis and Crohn's disease. Given the undoubted role of endogenous microflora in maintaining the integrity of the epithelium and controlling inflammation, as well as the potential toxicity of immunosuppressants used today, great hopes are placed on probiotics as “drugs of the future” in the treatment of inflammatory bowel diseases. Due to insufficient statistical material, the results of the conducted studies do not yet allow us to develop generally accepted recommendations for the inclusion of probiotics in standard circuits treatment. However, very encouraging data have been obtained regarding the ability of the complex probiotic VSL#3 to reduce the relapse rate of Crohn's disease. In ulcerative colitis, the effect in terms of maintaining remission was demonstrated by E. coli Nissle 1917 and Lactobacillus GG; from the point of view of remission induction - very high doses of probiotic VSL#3.
It should be understood that the administration of probiotics is rarely effective in the absence of etiotropic and pathogenetic treatment of the underlying disease. Depending on specific situation Surgical treatment may be required (for example, for adductor loop syndrome, interintestinal fistulas), prescription of anti-inflammatory and antibacterial drugs, regulators of gastrointestinal motility (for example, with irritable bowel syndrome).
Many probiotic preparations are registered in Russia. However, the vast majority of them are not sufficiently modern and do not contain species and strains of microorganisms for which evidence-based comparative studies have been obtained. As experience has accumulated, there has been a trend towards the use of combined probiotics.
Characteristics and application of Linex
IN recent years In the practice of Russian gastroenterologists, Linex, a combination drug containing bacteria - representatives of the natural intestinal microflora: Bifidobacterium infantis v. liberorum, Lactobacillus acidophilus and non-toxigenic group D lactic acid streptococcus – Streptococcus (Enterococcus) faecium. As noted above, these bacterial species have demonstrated clinical effectiveness in the treatment of a number of intestinal diseases and are among the microorganisms with which special “hopes” are associated for inclusion in the future in treatment regimens for chronic inflammatory bowel diseases. The cultures of microorganisms that make up Linex were obtained by growing on media with the addition of antibiotics, and therefore are resistant to most antibacterial agents and are able to reproduce even in conditions antibacterial therapy. The resistance of the resulting strains to antibiotics is so high that it persists after repeated inoculations of 30 generations, as well as in vivo. However, no transfer of antibacterial resistance genes to other types of microorganisms was observed. This is very important from the point of view of the consequences of using Linex: both while taking and after discontinuation of the drug, there is no danger of pathogenic bacteria and their own microflora developing resistance to antibiotics.
The therapeutic effect of Linex consists of temporarily replacing the functions of the patient’s own intestinal microflora in conditions of its suppression, in particular against the background of the use of antibiotics. The inclusion of lactobacilli, S. Faecium and bifidobacteria in Linex ensures the supply of “medicinal” microflora to different departments intestines in quantitatively and qualitatively balanced proportions.
In a placebo-controlled study involving 60 adult patients suffering from antibiotic-associated diarrhea or diarrhea of unknown etiology, taking Linex within 3-5 days was accompanied by normalization of stool. Demonstrated in children high efficiency Linexa in the prevention and treatment of already developed antibiotic-associated diarrhea.
The use of Linex against the background of Helicobacter eradication therapy improves the tolerability of antibiotics: it reduces the incidence of flatulence and diarrhea.
In the intestine, the microbial components of Linex not only have a eubiotic effect, but also perform all the functions of normal intestinal microflora: they participate in the synthesis of vitamins B1, B2, B3, B6, B12, H (biotin), PP, K, E, folic and ascorbic acids. By lowering the pH of the intestinal contents, they create favorable conditions for the absorption of iron, calcium, and vitamin D.
Lactobacilli and lactic acid streptococcus carry out enzymatic breakdown of proteins, fats and complex carbohydrates, including having a substitutive effect for lactase deficiency, which in most cases accompanies intestinal diseases.
Linex is produced in capsules containing at least 1.2 × 10 7 live lyophilized bacteria.
The pharmacokinetics of the drug has been little studied due to the fact that there are currently no pharmacokinetic models for studying complex biological substances in humans, consisting of components with different molecular weights.
Infants and children under 2 years old are prescribed Linex 1 capsule 3 times a day, children 2–12 years old – 1–2 capsules 3 times a day, children over 12 years old and adults – 2 capsules 3 times a day. The drug is taken after meals with a small amount of liquid. Do not drink hot drinks to avoid the death of living microflora.
Linex can be prescribed during pregnancy and breastfeeding. There are no reports of cases of Linex overdose.
Conclusion
Thus, probiotics, especially their combination preparations, are gradually occupying an increasingly stronger place in gastroenterology.
As the evidence base accumulates, they may provide doctors with a way to treat the patient, skillfully influencing his symbiosis with the world of bacteria and minimal risk to the human body.
Literature
Normal intestinal microorganisms are colonies of bacteria that populate the lumen of the lower digestive tract and the surface of the mucous membrane. They are needed for high-quality digestion of chyme (food bolus), metabolism and activation local protection against infectious pathogens, as well as toxic products.
Normal intestinal microflora– this is the balance of various microbes of the lower sections digestive system, that is, their quantitative and qualitative ratio necessary to maintain the biochemical, metabolic, immunological balance of the body and preserve human health.
The entire intestinal microflora is divided into:
Among all representatives there are anaerobes and aerobes. Their difference from each other lies in the peculiarities of their existence and life. Aerobes are microorganisms that can live and reproduce only in conditions of constant access to oxygen. Representatives of the other group are divided into 2 types: obligate (strict) and facultative (conditional) anaerobes. Both of them receive energy for their existence in the absence of oxygen. It is destructive for obligate anaerobes, but not for facultative ones, that is, microorganisms can exist in its presence.
These include gram-positive (bifidobacteria, lactobacilli, eubacteria, peptostreptococci) and gram-negative (bacteroides, fusobacteria, veillonella) anaerobes. This name is associated with the name of the Danish bacteriologist - Gram. He developed a special method for staining smears using aniline dye, iodine and alcohol. Under microscopy, some bacteria have a blue-violet color and are gram-positive. Other microorganisms become discolored. To better visualize these bacteria, a contrast dye (fuchsin) is used, which colors them pink. These are gram-negative microorganisms.
All representatives of this group are strict anaerobes. They form the basis of the entire intestinal microflora (92-95%). Beneficial bacteria produce antibiotic-like substances that help displace pathogens of dangerous infections from their environment. Also, normal microorganisms create an “acidification” zone (pH = 4.0-5.0) inside the intestine and form a protective film on the surface of its mucous membrane. Thus, a barrier is formed that prevents the colonization of foreign bacteria from outside. Beneficial microorganisms regulate balance opportunistic flora, preventing its excessive growth. Participate in the synthesis of vitamins.
These include gram-positive (clostridia, staphylococci, streptococci, bacilli) and gram-negative (Escherichia - Escherichia coli and other members of the Enterobacteriaceae family: Proteus, Klebsiella, Enterobacter, Citrobacter, etc.) facultative anaerobes. 
These microorganisms are opportunistic. That is, if there is well-being in the body, their influence is only positive, like that of normal microflora. Exposure to unfavorable factors leads to their excessive reproduction and transformation into pathogens. Develops with diarrhea, a change in the nature of the stool (liquid with an admixture of mucus, blood or pus) and a deterioration in general health. The quantitative growth of opportunistic microflora may be associated with weakened immunity, inflammatory diseases digestive system, poor nutrition and the use of medications (antibiotics, hormones, cytostatics, analgesics and other drugs).
The main representative of enterobacteria is with typical biological properties. It is able to activate the synthesis of immunoglobulins. Specific proteins interact with pathogenic microorganisms from the Enterobacteriaceae family and prevent their penetration into the mucous membrane. Besides this coli produces substances - colicins with antibacterial activity. That is, normal Escherichia is capable of inhibiting the growth and reproduction of putrefactive and pathogenic microorganisms from the family of enterobacteria - Escherichia coli with altered biological properties (hemolyzing strains), Klebsiella, Proteus and others. Escherichia takes part in the synthesis of vitamin K.
TO opportunistic microflora also include yeast-like fungi of the genus Candida. They are rarely found in healthy children and adults. Their detection in feces, even in small quantities, should be accompanied by clinical examination patient in order to exclude (excessive growth and proliferation of yeast-like fungi). This is especially true in young children and patients with reduced immunity.
These are bacteria that enter digestive tract from the outside and causing acute intestinal infections. Infection with pathogenic microorganisms can occur through consumption of contaminated food (vegetables, fruits, etc.) and water, violation of personal hygiene rules and contact with a sick person. Normally they are not found in the intestine. These include pathogenic causative agents of dangerous infections - pseudotuberculosis and other diseases. The most common representatives of this group are Shigella, Salmonella, Yersinia, etc. Some pathogens ( Staphylococcus aureus, Pseudomonas aeruginosa, atypical Escherichia coli) can be found among medical personnel (carriers of a pathogenic strain) and in hospitals. They cause serious hospital-acquired infections.
All pathogenic bacteria provoke the development of intestinal inflammation of the type or with stool disorder (diarrhea, mucus, blood, pus in the stool) and the development of intoxication of the body. Beneficial microflora is inhibited.
| Normal microorganisms | Children over 1 year old | Adults | ||
|---|---|---|---|---|
| Bifidobacteria | 10 9 –10 10 | 10 8 –10 10 | 10 10 –10 11 | 10 9 –10 10 |
| Lactobacilli | 10 6 –10 7 | 10 7 –10 8 | 10 7 –10 8 | >10 9 |
| Eubacteria | 10 6 –10 7 | >10 10 | 10 9 –10 10 | 10 9 –10 10 |
| Pepto-streptococci | <10 5 | >10 9 | 10 9 –10 10 | 10 9 –10 10 |
| Bacteroides | 10 7 –10 8 | 10 8 –10 9 | 10 9 –10 10 | 10 9 –10 10 |
| Fusobacteria | <10 6 | <10 6 | 10 8 –10 9 | 10 8 –10 9 |
| Veillonella | <10 5 | >10 8 | 10 5 –10 6 | 10 5 –10 6 |
CFU/g is the number of colony forming units of microbes in 1 gram of feces.
| Opportunistic microorganisms | Children under 1 year of age are breastfed | Children under 1 year of age on artificial feeding | Children over 1 year old | Adults |
|---|---|---|---|---|
| Escherichia coli with typical properties | 10 7 –10 8 | 10 7 –10 8 | 10 7 –10 8 | 10 7 –10 8 |
| Clostridia | 10 5 –10 6 | 10 7 –10 8 | < =10 5 | 10 6 –10 7 |
| Staphylococcus | 10 4 –10 5 | 10 4 –10 5 | <=10 4 | 10 3 –10 4 |
| Streptococci | 10 6 –10 7 | 10 8 –10 9 | 10 7 –10 8 | 10 7 –10 8 |
| bacilli | 10 2 –10 3 | 10 8 –10 9 | <10 4 | <10 4 |
| Fungi of the genus Candida | none | none | <10 4 | <10 4 |
Gram-positive strict anaerobes:
Gram-negative strict anaerobes:
A bacteriological examination of stool should be carried out by inoculating it on special nutrient media. The material is collected using a sterile spatula from the last portion of feces. The required volume of feces is 20 grams. The material for research is placed in sterile containers without preservatives. It is necessary to take into account the fact that anaerobic microorganisms must be reliably protected from the action of oxygen from the moment of stool collection until its inoculation. It is recommended to use test tubes filled with a special gas mixture (carbon dioxide (5%) + hydrogen (10%) + nitrogen (85%)) and a tightly ground lid. No more than 2 hours should pass from the moment the material is collected to the start of the bacteriological examination.
This stool analysis allows you to detect a wide range of microorganisms, calculate their ratio and diagnose visible disorders - dysbiosis. Disorders in the composition of the intestinal microflora are characterized by a decrease in the proportion of beneficial bacteria, an increase in the amount of opportunistic flora with a change in its normal biological properties, as well as the appearance of pathogens.
The imbalance of microorganisms is corrected using special preparations:
Thus, normal microflora with its specific functions - protective, metabolic and immunostimulating - determines the microbial ecology of the digestive tract and participates in maintaining the constancy of the internal environment of the body (homeostasis).
In the gastrointestinal tract – The human intestinal tract contains obligate (main microflora), facultative (opportunistic and saprophytic microflora) and transient microflora (microorganisms accidentally entering the gastrointestinal tract).
In the esophagus and stomach, transient microflora is usually detected, entering them with food or from the oral cavity. Despite the entry of a large number of microbes into the stomach, in healthy people a small number of microorganisms are normally detected in the stomach (less than 10 3 CFU/ml). This is due to the acidic pH value of the stomach contents and the bactericidal properties of gastric juice, which reliably protects a person from the penetration of pathogenic and conditionally pathogenic bacteria into the intestines. Gastric juice contains mainly acid-fast bacteria – lactobacilli, yeast fungi. In some people, streptococci are detected in it, S. ventriculus, B. subtilis, anaerobic gram-positive cocci.
In the thickness of the gastric mucosa, anaerobes veillonella, bacteroides, and peptococci are found.
In a study of healthy children aged 8 – For 15 years, staphylococci, streptococci, enterococci, corynebacteria, peptococci, lactobacilli and propionibacteria were identified in the antral mucosa of the stomach. Microbiological examination of stomach contents is carried out relatively rarely.
The number and composition of microbes in the small intestine varies depending on the part of the intestine. The total number of microbes in the small intestine is no more than 10 4 – 10 5 CFU/ml contents. The low concentration of microbes is due to the action of bile, the presence of pancreatic enzymes, and intestinal peristalsis, which ensures the rapid removal of microbes to the distal intestine; the production of immunoglobulins by mucosal cells, the state of the intestinal epithelium and mucus secreted by intestinal goblet cells containing microbial growth inhibitors. The microflora of the small intestine is represented predominantly by gram-positive facultative – anaerobic and anaerobic bacteria (enterococci, lactobacilli, bifidobacteria), yeast-like fungi, less common bacteroides and veillonella, and extremely rarely enterobacteria. After eating, the number of microbes in the small intestine may increase significantly, but then in a short time it quickly returns to its original level. In the lower parts of the small intestine (in the ileum), the number of microbes increases and can reach 10 7 CFU/ml of contents.
In the large intestine, the gram-positive flora changes to gram-negative. The number of obligate anaerobes begins to exceed the number of facultative anaerobes. Representatives of microbes characteristic of the large intestine appear.
The growth and development of microbes in the large intestine is facilitated by the absence of digestive enzymes, the presence of a large amount of nutrients, the presence of food for a long time, the structural features of the mucous membrane and, in particular, the mucous membranes of the large intestine. They determine the organ tropism of certain types of anaerobic bacteria, which, as a result of their vital activity, form products used by facultative anaerobic flora, which in turn create conditions for the life of obligate anaerobes.
More than 400 species of different microbes are present in the human large intestine, with the number of anaerobes being 100 – 1000 times the number of facultative anaerobes. Obligate anaerobes make up 90-95% of the total composition. They are represented by bifidobacteria, lactobacilli, bacteroides, veillonella, peptostreptococci, clostridia and fusobacteria (Fig. 1)
The share of other microorganisms accounts for 0.1 – 0.01% is residual microflora: enterobacteria (Proteus, Klebsiella, Serration), enterococci, staphylococci, streptococci, bacilli, yeast fungi (Fig. 3). Opportunistic amoebas, Trichomonas, and some types of intestinal viruses can live in the intestines.
Microflora of the gastrointestinal tract is a set of microorganisms located in the lumen of the gastrointestinal tract. The most microflora-populated organ is the large intestine. In each section of the gastrointestinal tract, the microflora has a different quantitative and qualitative composition. The bulk of beneficial flora is located in the lower intestines. Microflora can be both beneficial and pathogenic, which is significant for the health of the human body, because balance is necessary, because beneficial microflora is primarily responsible for good human immunity.
Beneficial flora are bifidobacteria and lactobacilli, which are responsible for normal intestinal function. Also, these beneficial bacteria protect the human body from the penetration of pathogenic foreign microbes and toxins, and accordingly promote the absorption of vitamins, digestion processes, and also strengthen the immune system.
If the gastrointestinal tract is functioning normally, then the intestinal microflora has a balance of pathogenic and beneficial microbes and bacteria. There are not many bacteria in the human stomach, since it has an acidic environment, their number is 103 species, the largest number of bacteria is located in the large intestine, their number is about 1013 species. If the balance of beneficial and pathogenic bacteria is disturbed, this leads to dysbiosis and other diseases.
The microflora of the digestive tract plays an important role in the body not only of humans, but also of animals. For example, animals also have microflora, the imbalance of which leads to diseases of the gastrointestinal tract.
Microbes are the most numerous representatives of our planet; they fill absolutely all the space available to them. In the process of evolution, microorganisms have adapted to exist in certain conditions, so-called econiches, and humans are one of them. Microorganisms have learned to coexist with humans, and not only to exist, but also to bring benefits - both to themselves and to their owner. Evolution has influenced the fact that certain types of microorganisms are able not only to live in the human intestine, but also to take care of his immune system, and also to be the main and irreplaceable link in the functioning of the digestive system.
Factors that contribute to overgrowth of intestinal flora:
The microflora of the gastrointestinal tract is divided into luminal and parietal flora; their composition is different. The composition of the wall flora is more stable and is represented mainly by lactobacilli and bifidobacteria, which protect the intestines from pathogenic bacteria. The composition of the luminal flora, in addition to lacto- and bifidobacteria, includes a number of other intestinal inhabitants.
Normal human flora is a single and coordinated mechanism; it is a sensitive indicator of the state of the human body when exposed to various factors.
The versatility of normal microflora is an important component of maintaining its composition. The qualitative and quantitative composition of microflora is influenced by a large number of different factors: these are environmental conditions (sanitary and hygienic, occupational, chemical, radiation and others), climatic and geographical conditions, quality and nature of nutrition, various immune disorders, physical inactivity, stress, and so on. ; The composition of the flora is also disrupted in various gastrointestinal diseases.
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Stages of formation of normal microflora of the gastrointestinal tract (GIT):
1) accidental contamination of the mucous membrane. Lactobacilli, clostridia, bifidobacteria, micrococci, staphylococci, enterococci, E. coli, etc. enter the gastrointestinal tract;
2) formation of a network of tape bacteria on the surface of the villi. Mostly rod-shaped bacteria are fixed on it, and the process of biofilm formation is constantly underway.
Traditionally, it was believed that the bile duct is sterile, and the presence of microorganisms in the bile is a marker of the pathological process. This assumption was confirmed by the failure to isolate bacterial strains from the normal bile duct. However, modern researchers substantiate the phenomenon of “normal microbiota of the biliary tract” as a separate functional layer of the wall of the biliary tract, which protects the biliary tract from colonization by exogenous microorganisms. Thus, clinical methods for maintaining the homeostasis of the normal biliary microbiota ecosystem can be used to prevent hepatobiliary diseases and treat inflammatory diseases of the biliary tract.
The esophagus does not normally contain microorganisms.
Microflora of the stomach. The microflora of the stomach is usually poor due to the acidic environment of gastric juice, which is destructive for many microorganisms. In the stomach - the habitat is extremely unpleasant - lactobacilli, yeast, occasionally staphylococci and sardines, spore-bearing bacilli, yeast can be found here. In the small intestine, the number of microbes is also small due to the bactericidal properties of its secretion. The large intestine is home to an abundant microflora, represented by intestinal microbes, enterococci and clostridia. Anaerobic non-spore-forming bacilli, bacteroids, aerobic bacilli, spirilla, fungi and staphylococci, streptococci, and lactic acid bacteria are also found here.
In the stomach, due to the acidic environment, the number of microbes is normal (lactobacillus, streptococcus, sarcina).
12 The intestine and proximal small intestine in healthy people are sterile due to the presence of aggressive digestive enzymes in them. In the distal part of the small intestine, 1 ml of contents contains 107-108 microbes, in equal numbers aerobic and anaerobic. In 1 ml of the contents of the distal colon there are 109−1012 microbes of about 400 species. The highest density of contamination is observed in the rectum. The stool microfauna is actually the fauna of the distal colon.
In healthy people in the duodenum, the number of bacteria is no more than 10 in 4 - 10 in 5 colony-forming units (cfu) per ml.
Intestinal microflora
– the concentration of microorganisms, their species composition and ratio varies depending on the intestinal section.
The human intestinal microflora consists of several hundred species, most of which are bacteria, such as E. coli. Other representatives of the microflora are microscopic fungi, in particular yeast, as well as protozoa.
Intestinal bacteria are capable of digesting complex carbohydrates and other substrates that are indigestible by humans, while producing vitamins and short-chain fatty acids (SCFA).
In order to study the functionality of the genes of representatives of the human intestinal microflora, two consortia were organized to study the human microbiota: China) established a catalog of 3.3 million predominant bacterial genes in the human intestinal metagenome.
In the first hours of life, a newborn's intestinal tract does not contain microbes. Then it is populated by microorganisms supplied with mother's milk. In a healthy child, predominantly lactic acid bacteria are found, which, after stopping breastfeeding, are replaced by E. coli and enterococci.
A third of the stool that forms in the large intestine consists of microbes.
Types of intestinal microflora
Parietal – constant in composition, performs the function of colonization resistance
Luminal - less constant in composition, performs enzymatic and immunizing functions.
Bifidobacteria are the most significant representatives of obligate bacteria in the intestine. These are anaerobes, do not form spores, are gram positive rods, the ends are forked, and may have spherical swellings. Most bifidobacteria are located in the large intestine, being its main parietal and luminal microflora. The content of bifidobacteria in adults is 10 in the 9th – 10 in the 10th cfu. on the city
Lactobacilli – another representative of the obligate microflora of the gastrointestinal tract is lactobacilli. These are gram positive rods, with pronounced polymorphism, arranged in chains or singly, and do not form spores. Lactoflor can be found in human and animal milk. Lactobacilli (lactobacillus). Content in the large intestine – 10 in the 6th – 10 in the 8th c.u. on the city
A representative of the obligate intestinal microflora is Escherichia coli (Escherichia coli). The content of E. coli is 10 to the 7th degree - 10 to the 8th degree c.u. on the city
Eobiosis – microflora – normal flora. The biological balance of normal flora is easily disturbed by factors of exogenous and endogenous nature.
Species composition - lactobacilli, bifidobacteria, bacteroides, entrococci, yeast-like fungi, etc. With food intake, the number of bacteria can increase significantly, but in a short time, returns to the original level.
In the upper small intestine– the number of microorganisms is 10 to 4 -10 to 5 colony-forming units per ml, in the ileum up to 10 to 8 degrees.
Mechanisms that inhibit microbial growth in the small intestine.
In the colon of a healthy person, the number of microorganisms is 10 in 11 - 10 in the 12th colony in the city. Anaerobic species of bacteria predominate - 90-95% of the total composition. These are bifidobacteria, bacteroides, lactobacteria, veillonella, peptostreptococci, clostridia.
About 5-10% are facultative anaerobes - and aerobes - Escherichia coli, lactose negative enterobacteria, enterococci, staphylococci, yeast-like fungi.
Importance for the body Research shows that the relationship between the gut and flora is not simply commensalism (that is, harmless coexistence), but rather a form of mutualism, that is, a mutually beneficial relationship. Although humans can survive without gut flora, microorganisms perform a number of beneficial functions for the host, such as anaerobic digestion of unused material to provide energy, training the immune system, and preventing the growth of harmful species. However, the intestinal fauna is not always exclusively beneficial; it is believed that some microorganisms can cause disease in certain cases.
Microorganisms
Bacteria that can be found in the human intestine
Bacteria Occurrence (%)
Bacteroides fragilis 100
Bacteroides melaninogenicus 100
Bacteroides oralis 100
Enterococcus faecalis 100
Escherichia coli 100
Enterobacter sp. 40–80
Klebsiella sp. 40–80
Bifidobacterium bifidum 30–70
Staphylococcus aureus 30–50
Lactobacillus 20–60
Clostridium perfringens 25–35
Proteus mirabilis 5–55
Clostridium tetani 1–35
Clostridium septicum 5–25
Pseudomonas aeruginosa 3–11
Salmonella enterica 3–7
Faecalibacterium prausnitzii - often
Peptostreptococcus sp. ?often
Peptococcus sp. ?often
Dysbacteriosis
Dysbacteriosis (dysbiosis) are any quantitative or qualitative changes in the normal human microflora typical for a given biotope, resulting from the impact of various unfavorable factors on a macro- or microorganism.
Microbiological indicators of dysbiosis are:
1) reduction in the number of one or more permanent species;
2) loss of certain characteristics by bacteria or acquisition of new ones;
3) increase in the number of transient species;
4) the appearance of new species unusual for this biotope;
5) weakening of the antagonistic activity of normal microflora.
The reasons for the development of dysbacteriosis can be:
1) antibiotic and chemotherapy;
2) severe infections;
3) severe somatic diseases;
4) hormone therapy;
5) radiation exposure;
6) toxic factors;
7) vitamin deficiency.
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Intestinal dysbiosis is a clinical and laboratory syndrome associated with changes in the qualitative and/or quantitative composition of the intestinal microflora, with the subsequent formation of metabolic and immunological disorders, with the possible development of gastrointestinal disorders.
Classification by species or group of organisms
Excess of staphylococci – staphylococcal dysbacteriosis
Dysbacteriosis caused by conditionally pathogenic enterobacteria, yeast-like fungi, associations of conditionally pathogenic microorganisms, etc.
Dysbacteriosis –
