Definition of the concept of infection, infectious process. Infections: general characteristics. Causative agents of surgical infection

Infection (lat. Infectio- I infect) is a state of infection caused by the interaction of an animal organism and a pathogenic microbe. The reproduction of pathogenic microbes that have invaded the body causes a complex of pathological and protective-adaptive reactions that are a response to the specific pathogenic action of the microbe. Reactions are expressed in biochemical, morphological and functional changes, in an immunological response and are aimed at maintaining constancy internal environment organism (homeostasis).

The state of infection, like any biological process, is dynamic. The dynamics of the reactions of interaction between micro - and macroorganisms is called the infectious process. On the one hand, the infectious process includes the introduction, reproduction and spread of the causative agent of the disease in the body, its pathogenic effect, and on the other hand, the body's response to this action. The body's response reactions, in turn, are conventionally divided into two groups (phases): infectious-pathological and protective-immunological.

Consequently, the infectious process constitutes the pathogenetic essence of an infectious disease.

The pathogenic (harmful) effect of the infectious agent in quantitative and qualitative terms may be unequal. In specific conditions, it manifests itself in some cases in the form of an infectious disease of varying severity, in others - without pronounced clinical signs, in still others - only by changes detected by microbiological, biochemical and immunological research methods. It depends on the quantity and quality of the specific pathogen that has penetrated the susceptible organism, the conditions of the internal and external environment determining the resistance of the animal and the nature of the interaction of micro - and macroorganisms.

By the nature of the interaction of the causative agent of the disease and the animal organism, three forms of infection are distinguished.

The first and most striking form of infection is an infectious disease. It is characterized by outward signs violations normal life organism, functional disorders and morphological tissue damage. An infectious disease that manifests itself with certain clinical signs is referred to as an overt infection. Often, an infectious disease does not manifest itself clinically or is hardly noticeable, and the infection remains latent (asymptomatic, latent, inapparent). However, in such cases, with the help of bacteriological and immunological research it is possible to identify the presence of an infectious process characteristic of this form of infection - a disease.

The second form of infection includes microcarriers, which are not associated with the previous illness of the animal. In such cases, the presence of an infectious agent in the organs and tissues of a clinically healthy animal does not lead to pathological condition and is not accompanied by immunological restructuring of the body. With microbearer, the existing balance between micro-and macroorganism is maintained natural factors resistance. This form of infection is established only by microbiological research... Microcarriers are quite often recorded in many diseases among healthy animals, both susceptible and non-susceptible (pathogens of swine erysipelas, pasteurellosis, clostridiosis, mycoplasmosis, malignant catarrhal fever, etc.). In nature, there are other types of microbearer (for example, convalescents and recovered animals), and they must be differentiated from an independent form of infection - microbearer by healthy animals.

The third form of infection is immunizing subinfection, in which microbes that enter the animal's body cause only a specific restructuring and immunity, but the pathogens themselves die. There are no functional disorders in the body and it does not become a source of the causative agent of infection. Immunizing subinfection, like microcarrier, is widespread in nature, but it has not yet been studied enough (for example, with leptospirosis, emkara, etc.), therefore it is difficult to control it when implementing antiepizootic measures.

Thus, the concept of "infection" is much broader than the concept of "infectious process" and "infectious disease". Differentiated approach to forms of infection makes it possible to correctly diagnose infectious diseases and maximally identify infected animals in a dysfunctional herd.

Infection- This is a state of contamination resulting from the penetration of microorganisms into a macroorganism.

Infectious process- this is the dynamics of the interaction between a micro- and a macroorganism.

If the pathogen and the animal's organism (host) meet, then this almost always leads to an infection or an infectious process, but not always - to an infectious disease with its clinical manifestations. Thus, the concepts of infection and infectious disease are not identical (the former is much broader).

Forms of infection :

Explicit infection or an infectious disease - the most striking, clinically pronounced form of infection. The pathological process is characterized by certain clinical and pathological signs.
Latent infection (asymptomatic, latent) - the infectious process does not manifest itself externally (clinically). But the causative agent of infection does not disappear from the body, but remains in it, sometimes in an altered form (L-form), retaining the ability to recover in bacterial form with its inherent properties.
Immunizing subinfection – the pathogen that has entered the body causes specific immune reactions, dies or is excreted; at the same time, the body does not become a source of the causative agent of infection, and functional disorders do not appear.
Microcarrier – the causative agent of the infection is present in the body of a clinically healthy animal. Macro and microorganisms are in a state of some balance.

Latent infection and microcarrier are not the same thing. At latent infection it is possible to determine the periods (dynamics) of the infectious process (occurrence, course and extinction), as well as the development of immunological reactions. With microbearer, this cannot be done.

For the occurrence of an infectious disease, a combination of the following factors is necessary:

the presence of a microbial agent;
the susceptibility of the macroorganism;
the presence of an environment in which this interaction takes place.

Forms of the course of an infectious disease :

Hyperacute (lightning-fast) current. In this case, the animal dies due to rapidly developing septicemia or toxinemia. Duration: several hours. Typical Clinical signs with this form they do not have time to develop.
Acute current . Duration: from one to several days. Typical clinical signs in this form appear violently.
Subacute course.Duration: longer than spicy. Typical clinical signs are less pronounced in this form. Pathological changes are typical.
Chronic course.Duration: can take months or even years. Typical clinical signs are weak or absent. The disease takes such a course when the pathogen does not have high virulence or the body is sufficiently resistant to infection.
Abortive course. With an abortive course, the development of the disease suddenly stops (breaks off) and recovery occurs. Duration: abortive illness is short-lived. It appears in mild form... Typical clinical signs are weak or absent. The reason for this course of the disease is considered increased resistance animal.

Periods (dynamics) of an infectious disease :

1st period - incubation (hidden) - from the moment the pathogen enters the body until the first, not yet clear clinical signs appear.

2nd period - preclinical (prodromal, harbingers of the disease) - continues from the moment the first, unclear, general clinical signs appear until their full development.

3rd period - clinical (full development of the disease, the height of the disease) - accompanied by the development of the main clinical signs characteristic of this disease.

4th period - extinction (clinical recovery, convalescence).

5th period - complete recovery.

Infection(Latin infectio - infection) is a combination of biological processes that arise and develop in the body when pathogenic microbes are introduced into it.

The infectious process consists of the introduction, reproduction and spread of the causative agent of the disease in the body, its pathogenic action, as well as the reaction of the macroorganism to this action.

There are three forms of infection:

1. An infectious disease characterized by disruption of the normal vital functions of the animal organism, organic, functional disorders and morphological tissue damage. An infectious disease may not manifest itself clinically or manifest itself subtly; then the infection is called latent, latent. In this case, an infectious disease can be diagnosed using various additional methods research.

2. Microbearer, not associated with the disease of the animal. The balance between the micro- and macroorganism is maintained due to the resistance of the macroorganism.

3. An immunizing infection is a relationship between a micro- and a macroorganism that causes only a specific restructuring in immunity. Functional disorders does not occur, the animal organism is not a source of the causative agent of infection. This form is widespread, but not well understood.

Commensalism- a form of cohabitation, when one of the organisms lives at the expense of the other, without causing him any harm. Commensal microbes include representatives normal microflora animal. With a decrease in the body's resistance, they can also exhibit a pathogenic effect.

Mutualism- a form of symbiosis, when both organisms derive mutual benefit from their cohabitation. A number of representatives of the normal microflora of animals are mutualists that benefit the owner.

The pathogenicity factors of microorganisms are divided into two groups, which determine:

invasiveness of microorganisms- the ability of microorganisms to penetrate through immunological barriers, skin, mucous membranes into tissues and organs, multiply in them and resist the immune forces of the macroorganism. Invasiveness is due to the presence of a capsule in the microorganism, mucus, surrounding the cell and resisting phagocytosis, flagella, pili, responsible for the attachment of microorganisms to the cell, and the production of enzymes hyaluronidase, fibrinolysin, collagenase, etc.;

toxigenicity- the ability of pathogenic microorganisms to produce exo- and endotoxins.

Exotoxins- products of microbial synthesis released by the cell into the environment. These are proteins with high and strictly specific toxicity. It is the action of exotoxins that determines the clinical signs of an infectious disease.

Endotoxins are part of the bacterial cell wall. They are released when the bacterial cell is destroyed. Regardless of the microbe-producer, endotoxins cause the same type of picture pathological process: weakness, shortness of breath, diarrhea, hyperthermia develop.

The pathogenic effect of viruses is associated with their multiplication in the cell of a living organism, leading to its death or to the elimination of its functional activity, but an abortive process is also possible - the death of the virus and the survival of the cell. Interaction with a virus can lead to cell transformation and the formation of tumors.

Each infectious agent has its own spectrum of pathogenicity, i.e. the circle of susceptible animals, where microorganisms realize their pathogenic properties.

There are obligate pathogenic microbes. The ability to cause an infectious process is their constant species feature. There are also facultative pathogenic (opportunistic) microorganisms, which, being commensals, cause infectious processes only when the resistance of their host is weakened. The degree of pathogenicity of microorganisms is called virulence. This is an individual characteristic of a specific, genetically homogeneous strain of a microbe. Virulence can vary depending on the conditions in which microorganisms exist.

In the case of acute infectious diseases, when infectious agents enter the body of a hardy animal, as a rule, the animal becomes ill.

Such pathogens fully satisfy the three conditions of the postulate of Henle and Koch:

1. The pathogen microbe must be detected in this disease and not be found in healthy people or in patients with other diseases.

2. The pathogen microbe must be isolated from the patient's body in its pure form.

3. A pure culture of the isolated microbe should cause the same disease in a susceptible animal.

Nowadays, this triad has largely lost its meaning.

A certain group of pathogens does not satisfy the Koch triad: they are isolated from healthy animals and from patients with other infectious diseases. They are low-virulent, and experimental reproduction of the disease in animals fails. The causal role of these pathogens is difficult to establish.

Types of infection. Depending on the method of infection, they are distinguished the following types infections:

exogenous - the causative agent of the infection enters the body from the environment;

endogenous, or autoinfection, - occurs when the protective properties of the body are weakened and the virulence of opportunistic microflora increases.

Depending on the spread of microorganisms in the body of animals, the following types of infection are distinguished:

local, or focal, infection - the causative agent of the disease multiplies at the site of its introduction into the body;

generalized - the causative agent of the disease from the site of introduction spreads throughout the body;

toxicoinfection - the pathogen remains at the site of its introduction into the body, and its exotoxins enter the bloodstream, exerting a pathogenic effect on the body (tetanus, infectious enterotoxemia);

toxicosis - exotoxins of microorganisms enter the body with food, they play the main pathogenetic role;

bacteremia / viremia - pathogens from the site of introduction enter the bloodstream and are transported by blood and lymph to various bodies and tissues multiply there too;

septicemia / sepsis - the multiplication of microorganisms occurs in the blood, and the infectious process is characterized by seeding of the whole organism;

pyemia - the pathogen spreads by the lymphogenous and hematogenous route during internal organs and multiplies in them not diffusely (bacteremia), but in separate foci, with an accumulation of pus in them;

septicopyemia is a combination of sepsis and pyemia.

The pathogen can cause various forms infectious disease depending on the ways of penetration and spread of microbes in the body of animals.

Dynamics of the infectious process. Infectious diseases differ from non-infectious ones in specificity, contagiousness, staging of the course and the formation of post-infectious immunity.

Specificity - an infectious disease is caused by a certain type of microorganism.

Contagiousness - the ability of an infectious disease to spread through the transmission of a pathogen from a sick animal to a healthy one.

The staging of the course is characterized by incubation, prodromal (preclinical) and clinical periods, the outcome of the disease.

The period from the moment the microbe enters the animal's body until the first symptoms of the disease appear is called incubation. It is not the same and ranges from one to two days (flu, anthrax, botulism) up to several weeks (tuberculosis), several months and years (slow viral infections).

In the prodromal period, the first nonspecific symptoms diseases - fever, anorexia, weakness, depression, etc. Its duration is from several hours to one or two days.

Infection is penetration and reproduction pathogenic microorganism(bacteria, virus, protozoa, fungus) in a macroorganism (plant, fungus, animal, human) that is susceptible to this kind microorganism. A microorganism capable of infection is called an infectious agent or pathogen.

Infection is primarily a form of interaction between a microbe and an affected organism. This process is extended in time and takes place only under certain environmental conditions. In an effort to emphasize the temporal extent of the infection, the term "infectious process" is used.

Infectious diseases: what are these diseases and how do they differ from non-infectious diseases

Under favorable environmental conditions, the infectious process takes on an extreme degree of its manifestation, at which certain clinical symptoms appear. This degree of manifestation is called an infectious disease. Infectious diseases differ from non-infectious pathologies in the following ways:

The cause of the infection is a living microorganism. Microorganism causing specific disease, called the causative agent of this disease;
Infections can be transmitted from an affected organism to a healthy one - this property of infections is called infectiousness;
Infections have a latent (latent) period - this means that they do not appear immediately after the pathogen enters the body;
Infectious pathologies cause immunological changes - they induce an immune response, accompanied by a change in the amount immune cells and antibodies, and also cause infectious allergies.

Rice. 1. Assistants of the famous microbiologist Paul Ehrlich with laboratory animals. At the dawn of the development of microbiology, laboratory vivariums were kept a large number of species of animals. Now they are often limited to rodents.

Factors of infectious diseases

So, for the occurrence of an infectious disease, three factors are required:

Microorganism-pathogen;
A host organism susceptible to it;
The presence of such environmental conditions in which the interaction between the pathogen and the host leads to the onset of the disease.

Infectious diseases can be caused by opportunistic microorganisms, which are most often representatives of normal microflora and cause the disease only with a decrease in immune defense.

Rice. 2. Candida - part of the normal microflora of the oral cavity; they cause disease only under certain conditions.

And pathogenic microbes, being in the body, may not cause a disease - in this case, they speak of the carrier of a pathogenic microorganism. In addition, laboratory animals are not always susceptible to human infections.

For the onset of an infectious process, it is important and enough microorganisms that enter the body, which is called the infectious dose. The susceptibility of the host organism is determined by its biological species, sex, heredity, age, nutritional adequacy and, most importantly, the state immune system and the presence of concomitant diseases.

Rice. 3. Plasmodium malaria can spread only in those territories where their specific carriers live - mosquitoes of the genus Anopheles.

Environmental conditions are also important, in which the development of the infectious process is maximally facilitated. Some diseases are seasonal, some microorganisms can only exist in certain climates, and some require vectors. V recent times the conditions of the social environment come to the fore: economic status, living and working conditions, the level of development of health care in the state, and religious characteristics.

Infectious process in dynamics

The development of infection begins with the incubation period. During this period, there are no manifestations of the presence of an infectious agent in the body, but the infection has already occurred. At this time, the pathogen multiplies to a certain number or releases a threshold amount of toxin. The duration of this period depends on the type of pathogen.

For example, with staphylococcal enteritis (a disease that occurs when eating contaminated food and is characterized by severe intoxication and diarrhea), the incubation period takes from 1 to 6 hours, and with leprosy it can stretch for decades.

Rice. 4. Incubation period leprosy can last for years.

In most cases, it lasts 2-4 weeks. Most often, the peak of infectivity occurs at the end of the incubation period.

The prodromal period is a period of precursors of the disease - vague, nonspecific symptoms such as headache, weakness, dizziness, change in appetite, fever. This period lasts 1-2 days.

Rice. 5. Malaria is characterized by a fever with special properties at different forms disease. By the form of the fever, one can assume the type of Plasmodium that caused it.

The prodrome is followed by the height of the disease, which is characterized by the appearance of the main clinical symptoms diseases. It can develop both rapidly (then they talk about sharp beginning), and slowly, sluggishly. Its duration varies depending on the state of the body and the capabilities of the pathogen.

Rice. 6. Typhoid Mary, who worked as a cook, was a healthy carrier of typhoid fever sticks. She infected typhoid fever more than half a thousand people.

For many infections, an increase in temperature is characteristic during this period, associated with the penetration of so-called pyrogenic substances into the blood - substances of microbial or tissue origin that cause fever. Sometimes the rise in temperature is associated with the circulation in the bloodstream of the pathogen itself - this condition is called bacteremia. If at the same time microbes also multiply, they speak of septicemia or sepsis.

Rice. 7. Yellow fever virus.

The end of the infectious process is called the outcome. There are the following outcomes:

Recovery;
Lethal outcome (death);
Transition to a chronic form;
Relapse (reoccurrence due to incomplete cleansing of the body from the pathogen);
The transition to a healthy microbearer (a person, without knowing it, carries pathogenic microbes and in many cases can infect others).

Rice. 8. Pneumocysts are fungi that are the leading cause of pneumonia in people with immunodeficiencies.

Classification of infections

Rice. 9. Oral candidiasis is the most common endogenous infection.

By the nature of the pathogen, bacterial, fungal, viral and protozoal (caused by protozoa) infections are isolated. By the number of types of pathogen, there are:

Monoinfections - caused by one type of pathogen;
Mixed, or mixed infections - caused by several types of pathogens;
Secondary - arising in the background already existing disease. A special case- opportunistic infections caused by opportunistic microorganisms against the background of diseases accompanied by immunodeficiencies.

By origin, they are distinguished:

Exogenous infections in which the pathogen enters from the outside;
Endogenous infections caused by microbes that were in the body before the onset of the disease;
Autoinfections - infections in which self-infection occurs by transferring pathogens from one place to another (for example, candidiasis oral cavity caused by the drift of fungus from the vagina with dirty hands).

According to the source of infection, the following are distinguished:

Anthroponoses (source - man);
Zoonoses (source - animals);
Anthropozoonoses (both a person and an animal can be a source);
Sapronoses (source - objects of the external environment).

According to the localization of the pathogen in the body, local (local) and general (generalized) infections are isolated. According to the duration of the infectious process, acute and chronic infections are distinguished.

Rice. 10. Mycobacterium leprosy. Leprosy is a typical anthroponosis.

Pathogenesis of infections: general scheme of development of the infectious process

Pathogenesis is a mechanism for the development of pathology. The pathogenesis of infections begins with the penetration of the pathogen through the entrance gate - mucous membranes, damaged integuments, through the placenta. Further, the microbe spreads throughout the body different ways: through the blood - hematogenous, through the lymph - lymphogenous, along the nerves - perineurally, along the length - destroying the underlying tissues, along physiological pathways- along, for example, the digestive or genital tract. The place of the final localization of the pathogen depends on its type and affinity for a certain kind fabrics.

Having reached the place of final localization, the pathogen has a pathogenic effect, damaging various structures mechanically, by waste products or the release of toxins. Excretion of the pathogen from the body can occur with natural secretions - feces, urine, phlegm, purulent discharge, sometimes with saliva, sweat, milk, tears.

Epidemic process

The epidemic process is the process of spreading infections among the population. The links in the epidemic chain include:

Source or reservoir of infection;
Transmission path;
Susceptible population.

Rice. 11. Ebola virus.

The reservoir differs from the source of infection in that the pathogen accumulates in it also between epidemics, and under certain conditions it becomes a source of infection.

The main routes of transmission of infections:

Fecal-oral - with food contaminated with infectious secretions, hands;
Airborne - through the air;
Transmissive - through the carrier;
Contact - sexual, touching, contact with contaminated blood, etc.;
Transplacental - from a pregnant mother to a child through the placenta.

Rice. 12. Influenza virus H1N1.

Transmission factors - objects that contribute to the spread of infection, for example, water, food, household items.

According to the coverage of the infectious process of a certain territory, they are distinguished:

Endemias - infections "tied" to a limited area;
Epidemics - infectious diseases covering large areas (city, region, country);
Pandemics are epidemics on the scale of several countries and even continents.

Infectious diseases account for the lion's share of all diseases faced by humanity... They are special in that with them a person suffers from the vital activity of living organisms, albeit thousands of times smaller than himself. Previously, they often ended fatally. Despite the fact that today the development of medicine has made it possible to significantly reduce mortality in infectious processes, it is necessary to be on the alert and know about the peculiarities of their occurrence and development.

Infection (infectio - infection) is the process of penetration of a microorganism into a macroorganism and its reproduction in it.

An infectious process is a process of interaction between a microorganism and a human body.

The infectious process has various manifestations: from asymptomatic carriage before infectious disease(with recovery or death).

An infectious disease is an extreme form of an infectious process.

An infectious disease is characterized by:

1) the presence of a certain live pathogen;

2) infectiousness, i.e. pathogens can be transmitted from a sick person to a healthy person, which leads to a wide spread of the disease;

3) the presence of a certain incubation period and a characteristic sequential change of periods during the course of the disease (incubation, prodromal, manifest (the height of the disease), recoalescence (recovery));

4) the development of clinical symptoms characteristic of this disease;

5) the presence of an immune response (more or less prolonged immunity after suffering a disease, the development allergic reactions in the presence of a pathogen in the body, etc.)

The names of infectious diseases are formed from the name of the pathogen (species, genus, family) with the addition of the suffixes "oz" or "az" (salmonellosis, rickettsiosis, amoebiasis, etc.).

The development of the infectious process depends on:

1) on the properties of the pathogen;

2) from the state of the macroorganism;

3) on environmental conditions that can affect both the state of the pathogen and the state of the macroorganism.

For any clinically manifest infectious disease, a distinction is made between next periods:

1. Incubation (latent) period (IP);

2. Period of precursors, or prodromal period;

3. The period of the main manifestations of the disease;

4. The period of extinction (decline of clinical manifestations) of the disease;

5. The period of convalescence (convalescence: early and late, with or without residual effects).

Incubation period- This is the time that passes from the moment of infection until the first signs of the disease appear. For each infectious disease, PI has its own duration, sometimes strictly defined, sometimes fluctuating; therefore, it is customary to distinguish the average duration of PI for each of them. During this period, the pathogen multiplies and the accumulation of toxins to a critical value occurs, when, according to this type of microbe, the first clinical manifestations disease. During IP, there are complex processes at the precellular and cellular levels, but there are still no organ and systemic manifestations of the disease.

Period of harbingers, or the prodromal period, is not observed in all infectious diseases and usually lasts 1-2-3 days. It is characterized by initial painful manifestations that do not have any characteristic clinical features characteristic of a particular infectious disease. Patients' complaints during this period are general malaise, mild headache, body aches and pains, chills, and mild fever.

The period of the main manifestations of the disease, the so-called "stationary" period, in turn, can be divided into a stage of increasing painful phenomena, the period of the height of the disease and its decline. During the growth and height of the disease, the main clinical manifestations appear in a certain sequence (stages), characterizing it as an independent clinically outlined disease. During periods of growth and height of the disease in the patient's body, the maximum accumulation of the pathogen and toxic substances associated with its vital activity: exo- and endotoxins, as well as nonspecific factors intoxication and inflammation. The effect of exotoxins on the human body, in comparison with endotoxins, is more definite, sometimes clearly local, with an inherent this disease damage to the anatomical structures of organs and tissues. The action of various endotoxins, although less differentiated, can still differ with different diseases not only by the degree of severity, but also by some features.

Convalescence period is manifested by a decrease in the severity of symptoms of the disease, especially fever. Decrease elevated temperature body can be fast (critical drop in temperature) and slow, gradual (lytic decrease in temperature). Patients have appetite, sleep is normalized, there is an increase in strength, restoration of body weight lost during illness; there is an interest in the environment, often capriciousness and increased exacting attention to oneself, which is associated with asthenization and violation adaptation mechanisms.

Depending on the number of participants infectious process types of pathogens infections are usually divided into mono- and polyinfection... V medical literature polyinfection is most often called mixed infections or mixed infections... TO

by duration, then here doctors distinguish sharp,subacute,chronic and slow infections. As a rule, most infections are acute, i.e. in the period of one month, during which all periods of the infectious process are realized. If the infectious process lasts up to three months, such infections are considered subacute, and if it lasts more than three months, they are considered chronic.

The importance of microorganisms in the occurrence of an infectious disease. Pathogenicity and virulence of microorganisms. Factors of pathogenicity, main groups and importance in the occurrence of an infectious disease. The concept of obligate pathogenic, opportunistic and non-pathogenic microorganisms.

Pathogenicity(from the Greek. pathos, disease + genos, birth) - it is the potential ability of microorganisms to cause disease, which is specific genetically determined trait.
Virulence (from lat. virulentus- poisonous, contagious) reflects the degree of pathogenicity, is a measure of the pathogenicity of the microbe. This property, an individual characteristic of each strain pathogenic microorganism. Strains of one type or another, based on this characteristic, can be subdivided into high-, moderately-, weakly virulent and avirulent(e.g. vaccine strains).
Determine the virulence of a particular culture strain in experiments in the infection of laboratory animals with the calculation DLM (Dosis letalis minima) - the dose of bacteria, viruses, toxins and other damaging agents that cause the death of 95% of the animals taken in the experiment. More accurate data on virulence and toxicity is given by DL50 (Dosis letalis 50), the dose of the investigated agent causing, under the given experimental conditions, a lethal effect in 50% of the animals taken into the experiment.

Pathogenic factors
Pathogenicity as biological trait bacteria is realized through their three properties: infectivity, invasiveness and toxigenicity.

Under infectivity (or infectivity) understand the ability of pathogens to enter the body and cause disease, as well as the ability of microbes to be transmitted using one of the transmission mechanisms, retaining their pathogenic properties in this phase and overcoming surface barriers (skin and mucous membranes). It is due to the presence in pathogens of factors that contribute to its attachment to the cells of the body and their colonization.
Under invasiveness understand the ability of pathogens to overcome defense mechanisms organism, multiply, penetrate its cells and spread in it.
Toxicity bacteria is due to the production of exotoxins by them. Toxicity due to the presence of endotoxins. Exotoxins and endotoxins have a peculiar effect and cause deep violations vital functions of the organism.

Infectious, invasive (aggressive) and toxigenic (toxic) properties are relatively unrelated to each other, they are manifested in different ways in different microorganisms.

Characterization of bacterial exotoxins. Molecular and cellular aspects of the action of exotoxins on the cells of a macroorganism. Structure and significance in development toxic effects bacterial lipopolysaccharides (LPS).

Lipopolysaccharide complexes of KS, mainly Gram-bacteria, are released only after the death of bacteria. Lipid A is considered an essential part of endotoxin, however toxic properties endotoxin is determined by the entire LPS molecule, since lipid A alone is less toxic than the whole LPS molecule. The formation of endotoxins is inherent in enterobacteria, brucella, rickettsia, and plague bacillus.

2. Less toxic than exotoxins.

3. Nonspecific: antibodies of low specificity are found in the blood serum of people who have been ill and during immunization of animals with various LPSs, and a similar clinical picture is observed.

4. Acting quickly.

5. Are haptens or weak antigens, have weak immunogenicity. The serum of an animal immunized with endotoxin has weak antitoxic activity and does not neutralize endotoxin.

6. They are thermostable, not inactivated by temperature; when heated, the activity of endotoxin increases.

7. They are not chemically inactivated (do not pass into toxoids when treated with formalin).

Exists physiological mechanisms the entry of very small (on the order of nanograms) amounts of endotoxin into the bloodstream. Absorbed in the large intestine and enters the liver, most of endotoxin is normally eliminated by phagocytes, but part of it enters the systemic circulation, causing a number of physiological effects.

When small doses of endotoxin enter the bloodstream, the following is observed:

stimulation of phagocytosis, increasing the body's resistance;
an increase in body temperature as a result of the action of the toxin on blood cells (granulocytes, monocytes), from which endogenous pyrogens (IL1) are released, acting on the hypothalamic thermoregulatory centers;
complement activation via an alternative pathway;
polyclonal stimulation and proliferation of B-lymphocytes, IgM synthesis;
implementation of antitumor immunity (TNF secretion);
activation of antiviral protection.

When large doses of endotoxin enter the bloodstream, infectious toxic shock (ITS) is a pronounced systemic reaction of the body as a result of exposure to endotoxins and bacterial products on cell membranes, blood coagulation components and complement. Gram flora more often causes ITS (in 70% of cases), it is more severe, mortality is higher (60 –90% for Gram etiology and 30–40% for Gram +).

TSS develops against the background of an increase in intoxication: the patient has weakness, shortness of breath, tachycardia, hypotension, chills, followed by a sharp rise in temperature, nausea, vomiting, diarrhea, and a state of prostration are often observed. ITS is manifested by impaired microcirculation, intravascular blood coagulation, and tissue necrosis. It often ends in fatal sepsis.

Symptoms of ITS may appear or worsen after the use of bactericidal antibiotics, which is associated with intensive bacteriolysis and the release of endotoxins (exacerbation of Herxheimer-Yarish-Lukashevich reaction or bacteriolysis reaction). This confirms the participation of the decay products of bacterial cells in the pathogenesis of shock. Therefore, at high risk participation of Gram bacteria as etiological factor and when the development of ITS is threatened, bacteriostatic antibiotics should be preferred.

Endotoxin shock is most demonstrative when meningococcal infection... Among the representatives of normal microflora, the main carrier of endotoxin is Gram - microorganisms of the family Bacteroidaceae. This reaction also occurs in infections that occur without shock. For example, when treating secondary fresh syphilis after the first injections of penicillin, patients have an increase in body temperature and increased inflammation in the area of syphilis - roseola acquire a more intense pink-red color. This is due to intensive lysis of the pallidum spirochete and increased immune responses to decay products.