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MOSCOW, September 7, Vladislav Strekopytov. Each of us is home to tens of trillions of microorganisms. Some perform very important functions — they participate in metabolic and immune processes. The role of others has not yet been clarified. Scientists regularly receive new data about this, and they do not always agree with generally accepted ideas.
The myth of microflora
The collection of microorganisms in the human body is often called microflora. But flora is plants. The community of bacteria, archaea, fungi, viruses and protozoa that exists in symbiosis with us is called microbiota, or microbiome.
They inhabit the skin, gastrointestinal tract, bile duct walls, mucous membranes, and all biological fluids of the body . They produce vitamins, help digest food, prevent the overgrowth of harmful bacteria, regulate the immune system, and even affect the brain. Microbiota is considered normal, that is, natural for the body, which under normal conditions does not cause disease.
The myth about the danger of microbes
In 1885, the German physician and bacteriologist Theodor Escherich discovered E. coli, which was named Escherichia coli in his honor. It is now one of the most well-studied model organisms. These bacteria are constantly in the intestines, they are necessary for humans, and their suppression (for example, when taking antibiotics) disrupts digestion. However, at first they thought that E. coli was a deadly pathogen.
The fact that the intestines contain microbes necessary for life was first suggested by the Russian biologist Ilya Mechnikov at the beginning of the 20th century. He was prompted to do this by the discovery of bifidobacteria in 1899. The theories of immunity, inflammation, and aging that he studied were based on the idea of the leading role of microorganisms. Mechnikov called for constant consumption of fermented milk products containing lactobacilli — he considered them the main means of combating aging and “self-poisoning” of the body.
August 17, 08:00
The myth of bad and good bacteria
Gradually a myth the idea that all microbes are harmful was replaced by the idea of the existence of beneficial and pathogenic microflora. In fact, microorganisms or their metabolites cannot be clearly “good” or “bad”. It all depends on the location and conditions.
For example, Escherichia coli in the intestines is useful: it synthesizes vitamin K and suppresses pathogenic microbes. And beyond it causes inflammation of organs and tissues. The microbe can enter the body through dirty water, unwashed hands, or unprocessed food. The main source of contamination is human and animal feces, as well as wastewater.
Clostridia bacteria Clostridioides difficile, like E. coli, are present in the human microbiome throughout life, usually without manifesting themselves. But when the immune system is weakened — in old age or during treatment with antibiotics — they can cause a severe infectious disease of the rectum.
The myth of dysbiosis
With many diseases, the composition of the microbiota changes — how usually with unpleasant symptoms. This is usually called dysbiosis, which is incorrect.
“Such changes are rarely permanent,” British microbiologists write in a recent review in Nature Microbiology. “The microbiota varies greatly in both health and disease. This makes it extremely difficult to profile the normal gut microbiota for clinical practice.”
Uninformative Scientists also consider analysis for intestinal biomarkers, which is offered by some treatment centers. For example, there is an opinion that the ratio of bacteria of the types Firmicutes and Bacteroidetes can be used to determine the tendency to obesity. However, this is not confirmed by anything.
The myth of tenfold superiority
One of the most common misconceptions: microbiota cells tenfold more than the body itself. This thesis was replicated for many years and even found its way into textbooks.
For many years, it was believed that the adult microbiome contains about 100 trillion bacterial cells, with ten trillion of its own. These indicators were first quantified in 2014 as part of the Human Microbiome Project, an initiative of the US National Institutes of Health. It turned out that there is approximately parity here.
The myth of two kilograms of bacteria
They also say that each of us has from one to two kilograms of bacteria. The authors of an article in Nature Microbiology showed that this is unlikely to be true either.
“Most of the human microbiota is found in the large intestine. Microorganisms usually account for no more than half the weight of feces, and the total contents of the colon range from 83 to 421 grams,” scientists calculate. “The average human stool weighs about 200 grams when wet.” In this case, the total weight of the microbiota definitely does not exceed 500 grams, but, most likely, it is much less.»
The myth of the inheritance of the microbiome
Often in the literature there is a statement that the intestinal microflora is inherited, since its composition is mainly formed at the prenatal stage. However, specialized research demonstrates that only a few types of bacteria pass directly from mother to child before or during birth and persist thereafter.
A dramatic increase in gut microbiota diversity occurs in the first few years of life. Therefore, every adult, even if they are identical twins, has a unique microbiome, by which it is theoretically possible to identify him.
By the age of three to four years, the assembly of the microbiome as a whole is completed, but it is subsequently affected by the environment, diets, past diseases, antibiotics and other factors.
The myth of the effect on the brain
There is a certain connection between the activity of bacteria in the intestines and neurons in the brain, which is called the “gut-brain” axis. Changes in the gut microbial community partially explain depression, memory loss, chronic fatigue syndrome, autism, schizophrenia and neurodegenerative disorders.
The microbiome sends signals through secreted chemicals to the central nervous system (CNS), affecting the brain and mental health. It has been proven, for example, that secondary bile acids of microbial origin produced in the intestine can affect cognitive function, and changes in their profile (decrease in the level of primary and increase in secondary cytotoxic bile acids) correlate with the development of dementia.
In this regard, there are often suggestions that increasing the number of “right” bacteria in the intestines will help cope with inflammation, reduce stress, and improve memory.
Scientists warn against such categoricalness. It is not always clear whether changes in the intestinal microbiome are the cause or result of the disease. Or both — as a consequence of cyclic feedback.
The intestine has its own system of neurons, which, on the one hand, is integrated into the general nervous system of the body, and on the other — in certain cases can function autonomously, sending signals to the central nervous system via the vagus nerve. It’s not for nothing that the intestines are sometimes called the “second brain.”
Scientists agree that much more work will be needed to gain a deeper understanding of the microbiome, but it is already clear that everything is very complicated.
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