home Endocrinology Bacteria - general characteristic. Classification, structure, nutrition and role of bacteria in nature. Bacteria Bacteria inside a person

Bacteria - general characteristic. Classification, structure, nutrition and role of bacteria in nature. Bacteria Bacteria inside a person

The most ancient living organism on our planet. Not only have its members survived for billions of years, but they are also powerful enough to wipe out every other species on Earth. In this article we will look at what types of bacteria there are.

Let's talk about their structure, functions, and also name some useful and harmful types.

Discovery of bacteria

Let's begin our excursion into the kingdom of microorganisms with a definition. What does "bacteria" mean?

The term comes from the ancient Greek word for "stick". Christian Ehrenberg introduced it into the academic lexicon. These are nuclear-free microorganisms that do not have a nucleus. Previously, they were also called “prokaryotes” (nuclear-free). But in 1970 there was a division into archaea and eubacteria. However, this concept is still more often used to mean all prokaryotes.

The science of bacteriology studies what types of bacteria there are. Scientists say that at this time about ten thousand different types of these living creatures have been discovered. However, it is believed that there are more than a million varieties.

Anton Leeuwenhoek, a Dutch naturalist, microbiologist and fellow of the Royal Society of London, in a letter to Great Britain in 1676, describes a number of the simplest microorganisms that he discovered. His message shocked the public, and a commission was sent from London to double-check this data.

After Nehemiah Grew confirmed the information, Leeuwenhoek became a world-famous scientist, a discoverer. But in his notes he called them “animalcules.”

Ehrenberg continued his work. It was this researcher who coined the modern term “bacteria” in 1828.

Microorganisms are also used for military purposes. With the help of various species, a deadly substance is created. For this, not only the bacteria themselves are used, but also the toxins released by them.

Peacefully, science uses single-celled organisms for research in genetics, biochemistry, genetic engineering and molecular biology. With the help of successful experiments, algorithms for the synthesis of vitamins, proteins and other substances necessary for humans were created.

Bacteria are used in other areas as well. With the help of microorganisms, ores are enriched and water bodies and soils are cleaned.

Scientists also say that the bacteria that make up the microflora in the human intestine can be called a separate organ with its own tasks and independent functions. According to researchers, there is about one kilogram of these microorganisms inside the body!

In everyday life, we encounter pathogenic bacteria everywhere. According to statistics, the largest number of colonies are found on the handles of supermarket trolleys, followed by computer mice in Internet cafes, and only in third place are the handles of public restrooms.

Beneficial bacteria

Even at school they teach what bacteria are. Grade 3 knows all kinds of cyanobacteria and other single-celled organisms, their structure and reproduction. Now we will talk about the practical side of the issue.

Half a century ago, no one even thought about such an issue as the state of microflora in the intestines. Everything was OK. Eating more natural and healthier, less hormones and antibiotics, less chemical emissions into the environment.

Today, in conditions of poor nutrition, stress, and an overabundance of antibiotics, dysbiosis and related problems are taking leading positions. How do doctors propose to deal with this?

One of the main answers is the use of probiotics. This is a special complex that repopulates the human intestines with beneficial bacteria.

Such an intervention can help with such unpleasant issues as food allergies, lactose intolerance, gastrointestinal disorders and other ailments.

Let's now touch on what beneficial bacteria there are, and also learn about their effect on health.

Three types of microorganisms have been studied in the most detail and are widely used to have a positive effect on the human body - acidophilus, Bulgarian bacillus and bifidobacteria.

The first two are designed to stimulate the immune system, as well as reduce the growth of some harmful microorganisms such as yeast, E. coli, and so on. Bifidobacteria are responsible for digesting lactose, producing certain vitamins and lowering cholesterol.

Harmful bacteria

Earlier we talked about what types of bacteria there are. The types and names of the most common beneficial microorganisms were announced above. Next we will talk about the “single-cell enemies” of humans.

There are some that are harmful only to humans, while others are deadly for animals or plants. People have learned to use the latter, in particular, to destroy weeds and annoying insects.

Before delving into what types there are, it is worth deciding on the ways of their distribution. And there are a lot of them. There are microorganisms that are transmitted through contaminated and unwashed food, by airborne droplets and contact, through water, soil or through insect bites.

The worst thing is that just one cell, once in the favorable environment of the human body, is capable of multiplying to several million bacteria within just a few hours.

If we talk about what types of bacteria there are, the names of pathogenic and beneficial ones are difficult for a layman to distinguish. In science, Latin terms are used to refer to microorganisms. In common parlance, abstruse words are replaced by concepts - “Escherichia coli”, “pathogens” of cholera, whooping cough, tuberculosis and others.

Preventive measures to prevent the disease are of three types. These are vaccinations and vaccinations, interruption of transmission routes (gauze bandages, gloves) and quarantine.

Where do bacteria in urine come from?

Some people try to monitor their health and get tested at the clinic. Very often the cause of poor results is the presence of microorganisms in the samples.

We'll talk about what bacteria are in urine a little later. Now it is worthwhile to dwell separately on where, in fact, single-celled creatures appear there.

Ideally, a person's urine is sterile. There cannot be any foreign organisms there. The only way bacteria can enter the waste is at the site where waste is removed from the body. In particular, in this case it will be the urethra.

If the analysis shows a small number of inclusions of microorganisms in the urine, then everything is normal for now. But when the indicator increases above the permitted limits, such data indicate the development of inflammatory processes in the genitourinary system. This may include pyelonephritis, prostatitis, urethritis and other unpleasant ailments.

Thus, the question of what types of bacteria are in the bladder is completely incorrect. Microorganisms do not enter the discharge from this organ. Scientists today have identified several reasons leading to the presence of single-celled creatures in urine.

Firstly, this is promiscuous sex life.
Secondly, diseases of the genitourinary system.
Thirdly, neglect of personal hygiene rules.
Fourthly, decreased immunity, diabetes and a number of other disorders.

Types of bacteria in urine

Earlier in the article it was said that microorganisms in waste are found only in cases of disease. We promised to tell you what bacteria are. The names will be given only of those species that are most often found in the analysis results.

So, let's begin. Lactobacillus is a representative of anaerobic organisms, a gram-positive bacterium. It must be in the human digestive system. Its presence in the urine indicates some malfunctions. Such an event is not critical, but it is an unpleasant wake-up call that you should take serious care of yourself.

Proteus is also a natural inhabitant of the gastrointestinal tract. But its presence in the urine indicates a failure in the excretion of feces. This microorganism passes from food into urine only in this way. A sign of the presence of a large amount of proteus in the waste is a burning sensation in the lower abdomen and painful urination when the liquid is dark in color.

Enterococcus fecalis is very similar to the previous bacterium. It gets into the urine the same way, multiplies quickly and is difficult to treat. In addition, enterococcus microorganisms are resistant to most antibiotics.

Thus, in this article we have figured out what bacteria are. We talked about their structure and reproduction. You have learned the names of some harmful and beneficial species.

Good luck, dear readers! Remember that following the rules of personal hygiene is the best prevention.

The totality of bacteria inhabiting the human body has a common name - microbiota. In a normal, healthy human microflora there are several million bacteria. Each of them plays an important role for the normal functioning of the human body.

In the absence of any type of beneficial bacteria, a person begins to get sick, the functioning of the gastrointestinal tract and respiratory tract is disrupted. Beneficial bacteria for humans are concentrated on the skin, in the intestines, and on the mucous membranes of the body. The number of microorganisms is regulated by the immune system.

Normally, the human body contains both beneficial and pathogenic microflora. Bacteria can be beneficial or pathogenic.

There are many more beneficial bacteria. They make up 99% of the total number of microorganisms.

In this situation, the necessary balance is maintained.

Among the different types of bacteria that live on the human body are:

bifidobacteria;
lactobacilli;
enterococci;
coli.

Bifidobacteria

This type of microorganism is the most common and is involved in the production of lactic acid and acetate. It creates an acidic environment, thereby neutralizing most pathogenic microbes. Pathogenic flora ceases to develop and cause processes of rotting and fermentation.

Bifidobacteria play an important role in a child’s life, since they are responsible for the presence of an allergic reaction to any food product. In addition, they have an antioxidant effect and prevent the development of tumors.

The synthesis of vitamin C is not complete without the participation of bifidobacteria. In addition, there is information that bifidobacteria help to absorb vitamins D and B, which are necessary for a person to function normally. If there is a deficiency of bifidobacteria, even taking synthetic vitamins of this group will not bring any results.

Lactobacilli

This group of microorganisms is also important for human health. Thanks to their interaction with other inhabitants of the intestine, the growth and development of pathogenic microorganisms is blocked and pathogens of intestinal infections are suppressed.

Lactobacilli are involved in the formation of lactic acid, lysocine, and bacteriocins. This is a great help for the immune system. If there is a deficiency of these bacteria in the intestines, then dysbiosis develops very quickly.

Lactobacilli populate not only the intestines, but also the mucous membranes. So these microorganisms are important for women's health. They maintain the acidity of the vaginal environment and prevent the development of bacterial vaginosis.

Escherichia coli

Not all types of E. coli are pathogenic. Most of them, on the contrary, perform a protective function. The usefulness of the genus E. coli lies in the synthesis of cocilin, which actively resists the bulk of pathogenic microflora.

These bacteria are useful for the synthesis of various groups of vitamins, folic and nicotinic acid. Their role in health should not be underestimated. For example, folic acid is essential for the production of red blood cells and maintaining normal hemoglobin levels.

Enterococci

This type of microorganism colonizes the human intestine immediately after birth.

They help absorb sucrose. Living mainly in the small intestine, they, like other beneficial non-pathogenic bacteria, provide protection against excessive proliferation of harmful elements. At the same time, enterococci are conditionally safe bacteria.

If they begin to exceed permissible limits, various bacterial diseases develop. The list of diseases is very long. Starting from intestinal infections, ending with meningococcal.

Positive effects of bacteria on the body

The beneficial properties of non-pathogenic bacteria are very diverse. As long as there is a balance between the inhabitants of the intestines and mucous membranes, the human body functions normally.

Most bacteria are involved in the synthesis and breakdown of vitamins. Without their presence, B vitamins are not absorbed by the intestines, which leads to disorders of the nervous system, skin diseases, and decreased hemoglobin.

The bulk of undigested food components that reach the large intestine are broken down precisely by bacteria. In addition, microorganisms ensure the constancy of water-salt metabolism. More than half of all microflora is involved in the regulation of the absorption of fatty acids and hormones.

The intestinal microflora forms local immunity. It is here that the bulk of pathogenic organisms are destroyed and the harmful microbe is blocked.

Accordingly, people do not feel bloating and flatulence. An increase in lymphocytes provokes active phagocytes to fight the enemy and stimulate the production of immunoglobulin A.

Beneficial non-pathogenic microorganisms have a positive effect on the walls of the small and large intestines. They maintain a constant level of acidity there, stimulate the lymphoid apparatus, the epithelium becomes resistant to various carcinogens.

Intestinal peristalsis also largely depends on what microorganisms are in it. Suppressing the processes of decay and fermentation is one of the main tasks of bifidobacteria. Many microorganisms develop for many years in symbiosis with pathogenic bacteria, thereby controlling them.

Biochemical reactions that constantly occur with bacteria release a lot of thermal energy, maintaining the overall thermal balance of the body. Microorganisms feed on undigested residues.

Dysbacteriosis

Dysbacteriosis is a change in the quantitative and qualitative composition of bacteria in the human body . In this case, beneficial organisms die, and harmful ones actively reproduce.

Dysbacteriosis affects not only the intestines, but also the mucous membranes (there may be dysbacteriosis of the oral cavity, vagina). The names that will prevail in the analyzes are: streptococcus, staphylococcus, micrococcus.

In normal conditions, beneficial bacteria regulate the development of pathogenic microflora. The skin and respiratory organs are usually under reliable protection. When the balance is disturbed, a person experiences the following symptoms: intestinal flatulence, bloating, abdominal pain, frustration.

Later, weight loss, anemia, and vitamin deficiency may begin. From the reproductive system there is abundant discharge, often accompanied by an unpleasant odor. Irritation, roughness, and cracks appear on the skin. Dysbacteriosis is a side effect after taking antibiotics.

If you notice such symptoms, you should definitely consult a doctor, who will prescribe a set of measures to restore normal microflora. This often requires taking probiotics.

Food poisoning suddenly affects a person or group of people who have eaten food, often quite benign in appearance. And despite the unchanged taste, color and smell, the dish that caused the poisoning contains a huge number of microbes that have multiplied in it and their toxins (poisons). Such microbial poisonings account for 90 percent of all food poisonings. Some of them are easy, others end tragically. Bacterial food poisoning is especially difficult for children, the elderly, and those suffering from chronic diseases of the digestive system.

First place in prevalence among bacterial food Salmonella infections are currently the main cause of poisoning. They affect not only people, but also animals: cattle, pigs, sheep, goats, horses, ducks, chickens, geese, turkeys—the main source of this infection. Animals become infected from each other if they are kept in a common pen. It happens that sick ducks or geese contaminate the water in the pond, and cows and horses drink it and also get sick with salmonellosis. The meat of sick animals is literally contaminated with salmonella. They also end up in animal milk and poultry eggs. Moreover, waterfowl eggs (ducks, geese) are especially dangerous, since salmonella is found not only on the outside of the shell, but also inside.

In addition to the so-called intravital contamination of meat, eggs, milk of sick animals and birds, secondary contamination of these products sometimes occurs after the slaughter of livestock or poultry. This happens when cutting a carcass, its improper storage and transportation, when it comes into contact with the meat of sick animals and birds. Meat and meat products are frequent (75-85 percent) culprits of food poisoning of a sapmonella nature.

Salmonella at home fall on various products when the housewife uses dishes, a meat grinder, knives, and a cutting board, first for processing raw meat and then for cooked foods. Improper storage of prepared foods in the refrigerator can also lead to salmonella contamination: in an unclosed container next to raw meat and other raw foods.

Dishes made from minced meat, especially jelly, pose a great danger.
The most powerful of all known bacterial poisons secretes the microbe botulinus, which is widespread in nature. It is found in the soil, in the intestines of fish and animals, and forms spores. The transformation of botulinus spores into microbes, their reproduction and destruction, and therefore the release of toxin, is possible, only without access to oxygen. That is why canned food creates the most favorable conditions for the germination of spores and the proliferation of microbes. Botulinus is unstable in the external environment, it dies at boiling temperatures, its reproduction is delayed in an acidic environment, but its spores are very resistant to heat, the action of chemicals and bactericidal substances.

They tolerate boiling for several hours. Preparing canned food at home in hermetically sealed jars does not destroy the spores. The only way to destroy them— heating in an autoclave at a temperature of 120 degrees and a certain pressure, which is only possible in the industrial production of canned food.

Among homemade canned foods, the most dangerous are mushrooms in hermetically sealed jars. This is due to the fact that it is difficult to thoroughly wash mushrooms from soil particles, which can also include botulinus spores. The following homemade canned foods are also the culprits of severe poisoning: eggplant and squash caviar, stuffed peppers, cucumbers, purslane, dill and parsley, apricot compote, which contain a small amount of natural acid.

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Bacteria are the most ancient organism on earth, and also the simplest in their structure. It consists of just one cell, which can only be seen and studied under a microscope. A characteristic feature of bacteria is the absence of a nucleus, which is why bacteria are classified as prokaryotes.

Some species form small groups of cells; such clusters may be surrounded by a capsule (case). The size, shape and color of the bacterium are highly dependent on the environment.

Bacteria are distinguished by their shape into rod-shaped (bacillus), spherical (cocci) and convoluted (spirilla). There are also modified ones - cubic, C-shaped, star-shaped. Their sizes range from 1 to 10 microns. Certain types of bacteria can actively move using flagella. The latter are sometimes twice the size of the bacterium itself.

Types of forms of bacteria

To move, bacteria use flagella, the number of which varies—one, a pair, or a bundle of flagella. The location of the flagella can also be different - on one side of the cell, on the sides, or evenly distributed throughout the entire plane. Also, one of the methods of movement is considered to be sliding thanks to the mucus with which the prokaryote is covered. Most have vacuoles inside the cytoplasm. Adjusting the gas capacity of the vacuoles helps them move up or down in the liquid, as well as move through the air channels of the soil.

Scientists have discovered more than 10 thousand varieties of bacteria, but according to scientific researchers, there are more than a million species in the world. The general characteristics of bacteria make it possible to determine their role in the biosphere, as well as to study the structure, types and classification of the bacterial kingdom.

Habitats

The simplicity of structure and speed of adaptation to environmental conditions helped bacteria spread over a wide range of our planet. They exist everywhere: water, soil, air, living organisms - all this is the most acceptable habitat for prokaryotes.

Bacteria were found both at the south pole and in geysers. They are found on the ocean floor, as well as in the upper layers of the Earth's air envelope. Bacteria live everywhere, but their number depends on favorable conditions. For example, a large number of bacterial species live in open water bodies, as well as soil.

Structural features

A bacterial cell is distinguished not only by the fact that it does not have a nucleus, but also by the absence of mitochondria and plastids. The DNA of this prokaryote is located in a special nuclear zone and has the appearance of a nucleoid closed in a ring. In bacteria, the cell structure consists of a cell wall, capsule, capsule-like membrane, flagella, pili and cytoplasmic membrane. The internal structure is formed by cytoplasm, granules, mesosomes, ribosomes, plasmids, inclusions and nucleoid.

The cell wall of a bacterium performs the function of defense and support. Substances can flow freely through it due to permeability. This shell contains pectin and hemicellulose. Some bacteria secrete a special mucus that can help protect against drying out. Mucus forms a capsule - a polysaccharide in chemical composition. In this form, the bacterium can tolerate even very high temperatures. It also performs other functions, such as adhesion to any surfaces.

On the surface of the bacterial cell there are thin protein fibers called pili. There may be a large number of them. Pili help the cell pass on genetic material and also ensure adhesion to other cells.

Under the plane of the wall there is a three-layer cytoplasmic membrane. It guarantees the transport of substances and also plays a significant role in the formation of spores.

The cytoplasm of bacteria is 75 percent made from water. Composition of the cytoplasm:

Metabolism in prokaryotes is possible both with and without the participation of oxygen. Most of them feed on ready-made nutrients of organic origin. Very few species are capable of synthesizing organic substances from inorganic ones. These are blue-green bacteria and cyanobacteria, which played a significant role in the formation of the atmosphere and its saturation with oxygen.

Reproduction

In conditions favorable for reproduction, it is carried out by budding or vegetatively. Asexual reproduction occurs in the following sequence:

The bacterial cell reaches its maximum volume and contains the necessary supply of nutrients.
The cell lengthens and a septum appears in the middle.
Nucleotide division occurs inside the cell.
The main and separated DNA diverge.
The cell divides in half.
Residual formation of daughter cells.

With this method of reproduction, there is no exchange of genetic information, so all daughter cells will be an exact copy of the mother.

The process of bacterial reproduction under unfavorable conditions is more interesting. Scientists learned about the ability of sexual reproduction of bacteria relatively recently - in 1946. Bacteria do not have division into female and reproductive cells. But their DNA is heterogeneous. When two such cells approach each other, they form a channel for the transfer of DNA, and an exchange of sites occurs - recombination. The process is quite long, the result of which is two completely new individuals.

Most bacteria are very difficult to see under a microscope because they do not have their own color. Few varieties are purple or green in color due to their bacteriochlorophyll and bacteriopurpurin content. Although if we look at some colonies of bacteria, it becomes clear that they release colored substances into their environment and acquire a bright color. In order to study prokaryotes in more detail, they are stained.

Classification

Classification of bacteria can be based on indicators such as:

Form
way to travel;
method of obtaining energy;
waste products;
degree of danger.

Bacteria symbionts live in community with other organisms.

Bacteria saprophytes live on already dead organisms, products and organic waste. They contribute to the processes of rotting and fermentation.

Rotting cleanses nature of corpses and other organic waste. Without the process of decay there would be no cycle of substances in nature. So what is the role of bacteria in the cycle of substances?

Rotting bacteria are an assistant in the process of breaking down protein compounds, as well as fats and other compounds containing nitrogen. After carrying out a complex chemical reaction, they break the bonds between the molecules of organic organisms and capture protein molecules and amino acids. When broken down, the molecules release ammonia, hydrogen sulfide and other harmful substances. They are poisonous and can cause poisoning in people and animals.

Rotting bacteria multiply quickly in conditions favorable to them. Since these are not only beneficial bacteria, but also harmful ones, in order to prevent premature rotting of products, people have learned to process them: drying, pickling, salting, smoking. All these treatment methods kill bacteria and prevent them from multiplying.

Fermentation bacteria with the help of enzymes are able to break down carbohydrates. People noticed this ability back in ancient times and still use such bacteria to make lactic acid products, vinegars, and other food products.

Bacteria, working together with other organisms, do very important chemical work. It is very important to know what types of bacteria there are and what benefits or harm they bring to nature.

Meaning in nature and for humans

The great importance of many types of bacteria (in the processes of decay and various types of fermentation) has already been noted above, i.e. fulfilling a sanitary role on Earth.

Bacteria also play a huge role in the cycle of carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, calcium and other elements. Many types of bacteria contribute to the active fixation of atmospheric nitrogen and convert it into organic form, helping to increase soil fertility. Of particular importance are those bacteria that decompose cellulose, which is the main source of carbon for the life of soil microorganisms.

Sulfate-reducing bacteria are involved in the formation of oil and hydrogen sulfide in medicinal mud, soils and seas. Thus, the layer of water saturated with hydrogen sulfide in the Black Sea is the result of the vital activity of sulfate-reducing bacteria. The activity of these bacteria in soils leads to the formation of soda and soda salinization of the soil. Sulfate-reducing bacteria convert nutrients in rice plantation soils into a form that becomes available to the roots of the crop. These bacteria can cause corrosion of metal underground and underwater structures.

Thanks to the vital activity of bacteria, the soil is freed from many products and harmful organisms and is saturated with valuable nutrients. Bactericidal preparations are successfully used to combat many types of insect pests (corn borer, etc.).

Many types of bacteria are used in various industries to produce acetone, ethyl and butyl alcohols, acetic acid, enzymes, hormones, vitamins, antibiotics, protein-vitamin preparations, etc.

Without bacteria, the processes of tanning leather, drying tobacco leaves, producing silk, rubber, processing cocoa, coffee, soaking hemp, flax and other bast-fiber plants, sauerkraut, wastewater treatment, leaching of metals, etc. are impossible.

There are approximately one hundred trillion cells in the human body, but only a tenth of them are human cells. The rest are microbes. They inhabit our skin, live in the nasopharynx, and throughout the intestines. Of course, they are 10-100 times smaller than human cells, but they greatly influence our lives.

This is what the bacteria that causes stomach ulcers looks like under a microscope. Long flagella at the rear end allow it not only to swim in the contents of the stomach, but also to “anchor” in its mucous membrane. The bacterium stimulates the secretion of hydrochloric acid, the stomach begins to digest itself, and the bacterium feeds on the products of this self-digestion. Nevertheless, sometimes it lives in the stomach of healthy people as a harmless symbiont and even, according to some scientists, brings some benefit, protecting people from food poisoning.

Symbiosis with humans is clearly beneficial for bacteria: we give them shelter with constant favorable conditions and abundant food. But they also give us something.

The contribution of microorganisms is most clearly revealed in experiments in which experimental animals are freed from symbiotic microflora. Mice removed from their mother's womb by Caesarean section and raised under sterile conditions have severely distended intestines. It is assumed that in order to digest food without the participation of symbiotic microbes, the intestines must be longer and thicker. Germ-free mice have longer microscopic villi that line the inner wall of the small intestine. Digested food is absorbed through these villi. There are fewer microscopic cavities in the intestinal wall where microbes typically live. There are fewer cells in the intestines that provide immunity. Even the number of nerves that control bowel movements is reduced. It is assumed that microbes to some extent control the development of the intestine, creating the conditions they need. An example of such interaction in development is known in leguminous plants: nitrogen-fixing microorganisms from the soil cause the plant to develop special nodules on the roots, in which they settle. The plant has the appropriate genes for nodule formation, but these genes do not appear unless they are stimulated by bacteria.

Germ-free mice are very susceptible to infection. In order to infect such a mouse, a hundred pathogenic microbes are enough, but for an ordinary mouse a hundred million are needed. Bacteria living in the intestines of ordinary mice physically block the invaders and even release an antibiotic to destroy them.

Bacteria living in the human intestines produce vitamin K, which is not synthesized by our body and is necessary for blood clotting. A number of other vitamins are also supplied by intestinal bacteria. In the intestines of ruminants live microbes that can digest plant cellulose and convert it into glucose, the lion's share of which goes to feed the animal itself. Some marine animals have luminous bacteria in their special glands, which make it easier to find prey or a mate with their light signals.

Recently, Swedish microbiologist Staffan Normark discovered that even the bacterium that causes stomach ulcers has some benefit. Its role in this disease was discovered more than ten years ago, but only now is it becoming clear why this bacterium is found in the stomach of many healthy people. It produces an antibiotic that protects against salmonella and other dangerous microorganisms. Apparently, in principle, this is a useful symbiont, which sometimes “goes crazy” and causes ulcerations of the stomach wall - perhaps in people with reduced immunity.