Definition of the concept “Infection is an infectious process. Infection definition

The infectious process is a complex process consisting of many components, which includes the interaction of various infectious agents with the human body. Among other things, it is characterized by the development of complex reactions, various shifts in the functioning of internal organs and organ systems, changes in hormonal status, as well as various immunological and resistance factors (nonspecific).

The infectious process is the basis for the development of any character. After heart diseases and cancer pathologies, nature, in terms of prevalence, occupy third place and, in connection with this, knowledge of their etiology is extremely important in medical practice.

The causative agents of infectious diseases include all kinds of microorganisms of animal or plant origin - lower fungi, rickettsia, bacteria, viruses, spirochetes, protozoa. An infectious agent is the primary and obligatory cause that leads to the occurrence of a disease. It is these agents that determine how specific the pathological condition will be and what the clinical manifestations will be. But you need to understand that not every penetration of an “enemy” agent will give rise to a disease. If the body's adaptation mechanism prevails over the damage mechanism, the infectious process will not be complete enough and a pronounced response of the immune system will occur, as a result of which the infectious agents will become inactive. The chance of such a transition depends not only on the state of the body’s immune system, but also on the degree of virulence, pathogenicity, as well as invasiveness and many other properties characteristic of the pathogenic microorganism.

The pathogenicity of microorganisms is their direct ability to cause the onset of disease.

The infection process is built in several stages:

Overcoming barriers of the human body (mechanical, chemical, environmental);

Colonization and adhesion by the pathogen to accessible cavities of the human body;

Reproduction of harmful agents;

Formation of protective reactions by the body to the harmful effects of a pathogenic microorganism;

It is precisely these periods of infectious diseases that any person most often goes through when “enemy” agents enter their body. Vaginal infections are also no exception and go through all these stages. It is worth noting that the time from the penetration of the agent into the body until the onset of the disease is called incubation.

Knowledge of all these mechanisms is extremely important, since infectious diseases are among the most common on the planet in terms of occurrence. In this regard, it is extremely important to understand all the features of infectious processes. This will allow not only to diagnose the disease in time, but also to choose the right treatment tactics for it.

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

Infectious process– the process of interaction between a microorganism and the human body.

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

Infectious disease- This is an extreme form of the infectious process.

An infectious disease is characterized by:

1) Availability certain live pathogen ;

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

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

4) development clinical symptoms characteristic of this disease ;

5) availability immune response (more or less long-lasting immunity after illness, development of 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.).

Development infectious process depends:

1) on the properties of the pathogen ;

2) on the state of the macroorganism ;

3) depending on environmental conditions , which can affect both the state of the pathogen and the state of the macroorganism.

Properties of pathogens.

The causative agents are viruses, bacteria, fungi, protozoa, helminths (their penetration is invasion).

Microorganisms that can cause infectious diseases are called pathogenic , i.e. pathogenic (pathos - suffering, genos - birth).

There are also opportunistic microorganisms that cause diseases with a sharp decrease in local and general immunity.

Infectious disease agents have properties pathogenicity And virulence .

Pathogenicity and virulence.

Pathogenicity– this is the ability of microorganisms to penetrate a macroorganism (infectivity), take root in the body, multiply and cause a complex of pathological changes (disturbances) in organisms sensitive to them (pathogenicity – the ability to cause an infectious process). Pathogenicity is a species-specific, genetically determined trait or genotypic trait.

The degree of pathogenicity is determined by the concept virulence. Virulence is a quantitative expression or pathogenicity. Virulence is phenotypic trait. This is a property of a strain that manifests itself under certain conditions (with variability of microorganisms, changes in the susceptibility of the macroorganism).

Quantitative indicators of virulence :

1) DLM(Dosis letalis minima) – minimum lethal dose– the minimum number of microbial cells that causes the death of 95% of susceptible animals under given specific experimental conditions (type of animal, weight, age, method of infection, time of death).

2) LD 50 – the amount that causes the death of 50% of experimental animals.

Since virulence is a phenotypic trait, it changes under the influence of natural causes. It can also be artificially change (up or down). Promotion carried out by repeated passaging through the body of susceptible animals. Demotion - as a result of exposure to unfavorable factors: a) high temperature; b) antimicrobial and disinfectants; c) growing on unfavorable nutrient media; d) defenses of the body - passage of slightly susceptible or unresponsive animals through the body. Microorganisms with weakened virulence are used to obtain live vaccines.

Pathogenic microorganisms also have specificity, organotropy and toxicity.

Specificity– ability to cause certain infectious disease. Vibrio cholerae causes cholera, Mycobacterium tuberculosis causes tuberculosis, etc.

Organotropy– the ability to infect certain organs or tissues (the causative agent of dysentery is the mucous membrane of the large intestine, the influenza virus is the mucous membrane of the upper respiratory tract, the rabies virus is the nerve cells of Ammon’s horn). There are microorganisms that can infect any tissue, any organ (staphylococci).

Toxicity– ability to form toxic substances. Toxic and virulent properties are closely related.

Virulence factors.

The characteristics that determine pathogenicity and virulence are called virulence factors. These include certain morphological(presence of certain structures - capsules, cell wall), physiological and biochemical signs(production of enzymes, metabolites, toxins that have an adverse effect on the macroorganism), etc. By the presence of virulence factors, pathogenic microorganisms can be distinguished from non-pathogenic ones.

Virulence factors include:

1) adhesins (provide adhesion) – specific chemical groups on the surface of microbes, which, like a “key to a lock,” correspond to the receptors of sensitive cells and are responsible for the specific adhesion of the pathogen to the cells of the macroorganism;

2) capsule – protection against phagocytosis and antibodies; bacteria surrounded by a capsule are more resistant to the action of the protective forces of the macroorganism and cause a more severe course of infection (pathogens of anthrax, plague, pneumococci);

3) surface-located substances of the capsule or cell wall of various natures (surface antigens): protein A of staphylococcus, protein M of streptococcus, Vi-antigen of typhoid bacilli, lipoproteins of gram “-” bacteria; they perform the functions of immune suppression and nonspecific protective factors;

4) aggression enzymes: proteases, destroying antibodies; coagulase, blood plasma clotting; fibrinolysin, dissolving fibrin clots; lecithinase, destroying lecithin membranes; collagenase, which destroys collagen; hyaluronidase, destroying hyaluronic acid of the intercellular substance of connective tissue; neuraminidase, destroying neuraminic acid. Hyaluronidase , breaking down hyaluronic acid, increases permeability mucous membranes and connective tissue;

toxins - microbial poisons - powerful factors of aggression.

Virulence factors provide:

1) adhesion – attachment or adhesion of microbial cells to the surface of sensitive cells of the macroorganism (to the surface of the epithelium);

2) colonization – reproduction on the surface of sensitive cells;

3) penetration – the ability of some pathogens to penetrate (penetrate) inside cells - epithelial, leukocytes, lymphocytes (all viruses, some types of bacteria: Shigella, Escherichia); in this case, the cells die, and the integrity of the epithelial cover may be disrupted;

4) invasion – the ability to penetrate through mucous and connective tissue barriers into underlying tissues (due to the production of the enzymes hyaluronidase, neuraminidase);

5) aggression - the ability of pathogens to suppress nonspecific and immune defenses of the host body and cause the development of damage.

Toxins.

Toxins are poisons of microbial, plant or animal origin. They have a high molecular weight and cause the formation of antibodies.

Toxins are divided into 2 groups: endotoxins and exotoxins.

Exotoxinsstand out into the environment during the life of a microorganism. Endotoxins tightly bound to the bacterial cell and stand out into the environment after cell death.

Properties of endo and exotoxins.

Exotoxins form the causative agents of the so-called toxinemic infections, which include diftheria, tetanus, gas gangrene, botulism, some forms of staphylococcal and streptococcal infections.

Some bacteria simultaneously produce both exo- and endotoxins (Escherichia coli, Vibrio cholerae).

Obtaining exotoxins.

1) growing a toxigenic (exotoxin-forming) culture in a liquid nutrient medium;

2)filtration through bacterial filters (separation of exotoxin from bacterial cells); Other cleaning methods can be used.

Exotoxins are then used to produce toxoids.

Obtaining toxoids.

1) 0.4% formalin is added to the exotoxin solution (filtrate of a broth culture of toxigenic bacteria) and kept in a thermostat at 39-40°C for 3-4 weeks; there is a loss of toxicity, but the antigenic and immunogenic properties are preserved;

2) add a preservative and adjuvant.

Anatoxins These are molecular vaccines. They are used for specific prevention of toxinemic infections , and to obtain therapeutic and prophylactic antitoxic serums, also used for toxinemic infections.

Obtaining endotoxins.

Various methods are used destruction of microbial cells , and then carry out cleaning, i.e. separation of endotoxin from other cell components.

Since endotoxins are lipopolysaccharides, they can be extracted from the microbial cell by destroying it with TCA (trichloroacetic acid) followed by dialysis to remove proteins.

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Chapter 1. Infection, infectious process, infectious disease

Infectious diseases are widespread throughout the world and are caused by various microorganisms. “Contagious” diseases have been known since ancient times; information about them can be found in the oldest written monuments: in the Indian Vedas, the works of Ancient China and Ancient Egypt. Descriptions of some infectious diseases, such as dysentery, tetanus, erysipelas, anthrax, viral hepatitis, etc., can be found in the writings of Hippocrates (460-377 BC). In Russian chronicles, infections were described under the name of epidemics, endemic pestilences, emphasizing the main feature - massiveness, high mortality and rapid spread among the population. Devastating epidemics and pandemics of infectious diseases were described. It is known that in the Middle Ages a plague epidemic (“Black Death”) raged, from which a third of the population of Europe died out, and throughout the world from the plague in the 14th century. More than 50 million people died. During the First World War, there was a flu pandemic (“Spanish flu”), which affected 500 million people, 20 million of them died. For a long time, nothing was known about the cause of infectious diseases; it was believed that these diseases arise in connection with “miasmas” - poisonous air fumes. This is the teaching in the 16th century. was replaced by the doctrine of “contagia” (Frakstoro). In the XVII-XIX centuries. Many childhood infections were described, such as measles, chicken pox, scarlet fever, etc. The full flowering of the study of infectious diseases occurred in the 19th century. during the period of rapid development of microbiology and the emergence of immunology in the twentieth century. (L. Pasteur, R. Koch, I. I. Mechnikov, L. Erlich, G. N. Minkh, D. K. Zabolotny, L. A. Zilber). Advances and achievements in microbiology contributed to the identification of infectious diseases as an independent science and the further development of teachings about the etiology, pathogenesis, symptoms, treatment and prevention of infectious diseases. The works of A. A. Koltypin, M. G. Danilevich, D. D. Lebedev, M. S. Maslov, S. D. Nosov and other scientists contributed to the development of childhood infections.

Infectious diseases are a large group of human diseases that arise as a result of exposure to viruses, bacteria and protozoa. They develop through the interaction of two independent biosystems - a macroorganism and a microorganism under the influence of the external environment, and each of them has its own specific biological activity.

Infection is the interaction of a macroorganism with a microorganism under certain conditions of the external and social environment, as a result of which pathological, protective, adaptive, compensatory reactions develop, which are combined into an infectious process. The infectious process is the essence of an infectious disease and can manifest itself at all levels of organization of the biosystem - submolecular, subcellular, cellular, tissue, organ, organism.

However, not every exposure to a pathogen causes disease. An infectious disease occurs when there is a disruption in body function and the appearance of a clinical picture. Thus, an infectious disease is an extreme degree of development of the infectious process. If, upon penetration of the pathogen into the body, a clinical picture does not form, then they speak of a healthy carriage, which can occur in children with residual specific immunity or in people with congenital natural immunity. There is also convalescent carriage, which occurs during the period of recovery from an infectious disease. Depending on the conditions of infection, the properties of the infectious agent, the state of the macroorganism (susceptibility, degree of specific and nonspecific reactivity), several forms of interaction of the microorganism with the human body have been described.

Manifest forms (manifested clinically) are divided into acute and chronic. There are also typical, atypical and fulminant forms, which usually end in death. Based on severity, they are divided into mild, moderate and severe forms.

In the acute form of a clinically manifested infection, the pathogen remains in the body for a short time. This form is characterized by a high intensity of release of pathogens into the environment by patients, which creates a high infectiousness of patients. Many infectious diseases occur in acute form, for example plague, smallpox, scarlet fever. Others, both acute and chronic, include brucellosis, hepatitis B, and dysentery.

The chronic form of the disease is characterized by a longer stay of the pathogen in the body, frequent exacerbations and remissions of the pathological process and, in the case of timely treatment, a favorable outcome and recovery, as in the acute form.

Repeated illness due to infection with the same infectious agent is called reinfection. If infection with another infectious agent occurs before recovery from the disease, then they speak of superinfection.

Bacterial carriage is a process that occurs asymptomatically in acute or chronic form. Pathogens are present in the body, but the process does not manifest itself, and outwardly the person remains healthy. Immunological changes are detected in the body, as well as functional morphological disorders in organs and tissues, typical for this disease.

The subclinical form of infection is of great epidemiological significance, since such patients are a reservoir and source of pathogens with preserved ability to work and social activity, which complicates the epidemic situation. However, the high frequency of subclinical forms of some infections (dysentery, meningococcal infection, influenza, etc.) contributes to the formation of a massive immune layer among people, which to a certain extent stops the spread of these infectious diseases.

Overlatent (latent) infection occurs as a result of long-term asymptomatic interaction of a macroorganism with a microorganism. At its core, it is a chronic infectious disease with a benign course; it occurs in diseases such as hepatitis B, herpetic infection, typhoid fever, cytomegalovirus infection and many others. etc. This form is more common in children with reduced cellular and humoral immunity, while the infectious agent is either in a defective state or in a special stage of its life activity (L - form). The formation of L - forms occurs under the influence of the body’s protective immune forces and medications (antibiotics). Atypical strains are formed with changes in all properties of the microorganism.

A significantly new form of interaction between infection and the human body is slow infection. It is characterized by a long (up to several years) incubation period - a stage at which there is no disease. At the same time, the disease steadily progresses with the development of severe disorders in many organs and systems (most often in the nervous system), and death is often observed. This type of infection includes: AIDS, congenital rubella, chronic active hepatitis with transition to cirrhosis, etc.

Infectious diseases resulting from infection by microorganisms of one type are called monoinfections. When infected with bacteria of different types - mixed, or mixed infection. One of the variants of a mixed infection is a secondary infection, in which a new one is added to an existing disease.

The infectious process can occur due to the activation of saprophytic microflora, i.e. those microbes that constantly live on the skin and mucous membranes. In these cases, we talk about endogenous or autoinfection, which most often occurs in weakened children with chronic diseases, in children who have been receiving antibacterial or cytostatic (immune suppressive) therapy for a long time.

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Part I. Infectious diseases. basic conceptsChapter 2. Causative agent of an infectious disease

The environment is filled with a huge number of “inhabitants”, among which there are various microorganisms: viruses, bacteria, fungi, protozoa. They can live in absolute harmony with humans (non-pathogenic), exist in the body without causing harm under normal conditions, but become activated under the influence of certain factors (conditionally pathogenic) and be dangerous to humans, causing the development of a disease (pathogenic). All these concepts relate to the development of the infectious process. What is an infection, what are its types and features - is discussed in the article.

Basic Concepts

An infection is a complex of relationships between different organisms, which has a wide range of manifestations - from asymptomatic carriage to the development of the disease. The process appears as a result of the introduction of a microorganism (virus, fungus, bacteria) into a living macroorganism, in response to which a specific protective reaction occurs on the part of the host.

Features of the infectious process:

1. Contagiousness is the ability to quickly spread from a sick person to a healthy person.
2. Specificity - a certain microorganism causes a specific disease, which has characteristic manifestations and localization in cells or tissues.
3. Periodicity - each infectious process has periods of its course.

Periods

The concept of infection is also based on the cyclical nature of the pathological process. The presence of periods in development is characteristic of each similar manifestation:

1. The incubation period is the time that passes from the moment the microorganism is introduced into the body of a living being until the first clinical signs of the disease appear. This period can last from several hours to several years.
2. The prodromal period is the appearance of a general clinical picture characteristic of most pathological processes (headache, weakness, fatigue).
3. Acute manifestations are the peak of the disease. During this period, specific symptoms of infection develop in the form of rashes, characteristic temperature curves, and tissue damage at the local level.
4. Convalescence is the time of fading of the clinical picture and recovery of the patient.

Types of infectious processes

To consider in more detail the question of what an infection is, you need to understand what it is like. There are a significant number of classifications depending on the origin, course, localization, number of microbial strains, etc.

1. According to the method of penetration of pathogens:

• - characterized by the penetration of a pathogenic microorganism from the external environment;
• endogenous process - activation of one’s own opportunistic microflora occurs under the influence of unfavorable factors.

2. By origin:

• spontaneous process - characterized by the absence of human intervention;
• experimental - the infection was bred artificially in a laboratory.

3. By the number of microorganisms:

• monoinfection - caused by one type of pathogen;
• mixed - several types of pathogens are involved.

4. By order:

• primary process - a newly emerging disease;
• secondary process - accompanied by the addition of additional infectious pathology against the background of the primary disease.

5. By localization:

• local form - the microorganism is found only in the place through which it entered the host’s body;
• - pathogens spread throughout the body with further settling in certain favorite places.

6. Downstream:

• acute infection - has a clear clinical picture and lasts no more than a few weeks;
• chronic infection - characterized by a sluggish course, can last for decades, has exacerbations (relapses).

7. By age:

• "children's" infections - affect children mainly aged 2 to 10 years (chicken pox, diphtheria, scarlet fever, whooping cough);
• There is no concept of “adult infections” as such, since the child’s body is just as sensitive to those pathogens that cause the development of the disease in adults.

There are concepts of reinfection and superinfection. In the first case, a person who has fully recovered, after an illness, becomes infected again with the same pathogen. With superinfection, re-infection occurs during the course of the disease (strains of the pathogen are layered on top of each other).

Paths of entry

There are the following routes of penetration of microorganisms that ensure the transfer of pathogens from the external environment to the host organism:

• fecal-oral (consists of nutritional, water and contact-household);
• transmissible (blood) - includes sexual, parenteral and through insect bites;
• aerogenic (airborne dust and airborne droplets);
• contact-genital, contact-wound.

Most pathogens are characterized by the presence of a specific route of penetration into the macroorganism. If the transmission mechanism is interrupted, the disease may not appear at all or may worsen in its manifestations.

Localization of the infectious process

Depending on the area affected, the following types of infections are distinguished:

1. Intestinal. The pathological process occurs in parts of the gastrointestinal tract, the pathogen penetrates through the fecal-oral route. These include salmonellosis, dysentery, rotavirus, and typhoid fever.
2. Respiratory. The process occurs in the upper and lower respiratory tract, microorganisms “move” in most cases through the air (influenza, adenoviral infection, parainfluenza).
3. External. Pathogens contaminate the mucous membranes and skin, causing fungal infections, scabies, microsporia, and STDs.
4. enters through the blood, spreading further throughout the body (HIV infection, hepatitis, diseases associated with insect bites).

Intestinal infections

Let us consider the features of pathological processes using the example of one of the groups - intestinal infections. What is an infection that affects the human gastrointestinal tract, and what is its difference?

Diseases of this group can be caused by pathogens of bacterial, fungal and viral origin. Viral microorganisms that can penetrate various parts of the intestinal tract are rotaviruses and enteroviruses. They can spread not only through the fecal-oral route, but also through airborne droplets, affecting the epithelium of the upper respiratory tract and causing herpes sore throat.

Bacterial diseases (salmonellosis, dysentery) are transmitted exclusively by the fecal-oral route. Infections of fungal origin occur in response to internal changes in the body that occur under the influence of long-term use of antibacterial or hormonal drugs, with immunodeficiency.

Rotaviruses

Rotavirus intestinal infection, the treatment of which must be comprehensive and timely, in principle, like any other disease, makes up half of the clinical cases of viral intestinal infectious pathologies. An infected person is considered dangerous to society from the end of the incubation period until complete recovery.

Intestinal rotavirus is much more severe than in adults. The stage of acute manifestations is accompanied by the following clinical picture:

• abdominal pain;
• diarrhea (the stool is light in color and may contain blood);
• bouts of vomiting;
• hyperthermia;
• runny nose;
• inflammatory processes in the throat.

Rotavirus in children is in most cases accompanied by outbreaks of the disease in school and preschool institutions. By the age of 5, most children have experienced the effects of rotaviruses. Subsequent infections are not as severe as the first clinical case.

Surgical infection

Most patients in need of surgical intervention are interested in the question of what a surgical-type infection is. This is the same process of interaction between the human body and a pathogenic pathogen, only occurring during surgery or requiring surgical intervention to restore functions in a certain disease.

There are acute (purulent, putrefactive, specific, anaerobic) and chronic processes (specific, nonspecific).

Depending on the location of the surgical infection, the following diseases are distinguished:

• soft tissues;
• joints and bones;
• brain and its structures;
• abdominal organs;
• organs of the chest cavity;
• pelvic organs;
• individual elements or organs (breast, hand, foot, etc.).

Pathogens of surgical infection

Currently, the most frequent “guests” of acute purulent processes are:

• staphylococcus;
• Pseudomonas aeruginosa;
• enterococcus;
• coli;
• streptococcus;
• Proteus.

The entrance gates for their penetration are various damage to the mucous membranes and skin, abrasions, bites, scratches, ducts of the glands (sweat and sebaceous). If a person has chronic foci of accumulation of microorganisms (chronic tonsillitis, rhinitis, caries), then they cause the spread of pathogens throughout the body.

Treatment of infection

The basis of getting rid of pathological microflora is aimed at eliminating the cause of the disease. Depending on the type of pathogen, the following groups of medications are used:

1. Antibiotics (if the causative agent is a bacterium). The choice of a group of antibacterial agents and a specific drug is made on the basis of bacteriological examination and determination of the individual sensitivity of the microorganism.
2. Antiviral (if the causative agent is a virus). At the same time, drugs are used that strengthen the human body’s defenses.
3. Antimycotic agents (if the pathogen is a fungus).
4. Antihelminthic (if the pathogen is a helminth or a protozoan).

Treatment of infections in children under 2 years of age is carried out in a hospital setting to avoid the development of possible complications.

Conclusion

After the occurrence of a disease that has a specific pathogen, the specialist differentiates and determines the need for hospitalization of the patient. The specific name of the disease must be indicated in the diagnosis, and not just the word “infection”. The medical history, which is taken for inpatient treatment, contains all the data about the stages of diagnosis and treatment of a specific infectious process. If there is no need to hospitalize the patient, all such information is recorded in the outpatient card.

Historically, the word “infection” ” (lat. inficio - to infect) was first introduced to refer to venereal diseases.

Infection- the totality of all biological phenomena and processes that occur in the body during the introduction and reproduction of microorganisms in it, the result of the relationship between the macro- and the microorganism in the form of adaptation and pathological processes in the body, i.e. infectious process.

Infectious disease- the most pronounced form of the infectious process.

Term infection or synonym infectious process means a set of physiological and pathological regenerative and adaptive reactions that occur in a susceptible macroorganism under certain environmental conditions as a result of its interaction with pathogenic or conditionally pathogenic bacteria, fungi and viruses that have penetrated and multiplied in it and are aimed at maintaining the constancy of the internal environment of the macroorganism (homeostasis). A similar process, but caused by protozoa, helminths and insects - representatives of the kingdom Animalia, is called invasion.

Occurrence, course and outcome of the infectious process determined by three groups of factors: 1) quantitative and qualitative characteristics of the microbe - the causative agent of the infectious process; 2) the state of the macroorganism, the degree of its susceptibility to the microbe; 3) the action of physical, chemical and biological factors of the external environment surrounding the microbe and macroorganism, which determines the possibility of establishing contacts between representatives of different species, the common habitat of different species, food connections, population density and size, features of the transfer of genetic information, features of migration, etc. etc. In this case, in relation to a person, environmental conditions should first of all be understood social conditions his life activity. The first two biological factors are direct participants in the infectious process that develops in the macroorganism under the influence of a microbe. At the same time, the microbe determines the specificity of the infectious process, and the decisive integral contribution to the form of manifestation of the infectious process, its duration, severity of manifestations and outcome is made by the state of the macroorganism, primarily by the factors of its nonspecific resistance, which are assisted by factors of specific acquired immunity. The third, environmental, factor has an indirect effect on the infectious process, reducing or increasing the susceptibility of the macroorganism, or reducing or increasing the infectious dose and virulence of the pathogen, activating infection mechanisms and the corresponding routes of transmission, etc.

Mutualism- mutually beneficial relationships (for example, normal microflora).

Commensalism- one partner (the microbe) benefits without causing much harm to the other. It should be noted that with any type of relationship, a microorganism can manifest its pathogenic properties (for example, opportunistic commensal microbes in an immunodeficient host).

Pathogenicity(“disease-giving”) - the ability of a microorganism to cause disease. This property characterizes species genetic characteristics of microorganisms, their genetically determined characteristics, allowing them to overcome the host’s defense mechanisms and manifest their pathogenic properties.

Virulence - phenotypic(individual) quantitative expression of pathogenicity (pathogenic genotype). Virulence can vary and can be determined by laboratory methods (more often - DL50 - 50% lethal dose - the number of pathogenic microorganisms that can cause the death of 50% of infected animals).

Based on their ability to cause disease, microorganisms can be divided into pathogenic, opportunistic, non-pathogenic. Opportunistic microorganisms are found both in the environment and as part of normal microflora. Under certain conditions (immunodeficiency states, injuries and operations with the penetration of microorganisms into tissues) they can cause endogenous infections.

3) Factors of pathogenicity of microorganisms: adhesins. Factors of invasion and aggression. Microbial tropism. Relationship between microbial cell structure and pathogenicity factors.

Main factors of pathogenicity of microorganisms- adhesins, pathogenicity enzymes, substances that suppress phagocytosis, microbial toxins, under certain conditions - capsule, microbial motility. Virulence is associated with toxicogenicity(the ability to form toxins) and invasiveness(the ability to penetrate host tissue, multiply and spread). Toxigenicity and invasiveness have independent genetic control and are often inversely related (a pathogen with high toxicity may have low invasiveness and vice versa).

Adhesins and colonization factors - more often, the surface structures of a bacterial cell, with the help of which bacteria recognize receptors on cell membranes, attach to them and colonize tissues. The adhesion function is performed pili, outer membrane proteins, LPS, teichoic acids, viral hemagglutinins. Adhesion is a trigger for the realization of pathogenic properties of pathogens.

Factors of invasion, penetration into host cells and tissues. Microorganisms can multiply outside cells, on cell membranes, and inside cells. Bacteria secrete substances that help overcome host barriers, penetrate and reproduce. In gram-negative bacteria these are usually outer membrane proteins. These same factors include pathogenicity enzymes.

Pathogenicity enzymes- these are factors of aggression and protection of microorganisms. The ability to form exoenzymes largely determines the invasiveness of bacteria - the ability to penetrate mucous, connective tissue and other barriers. These include various lytic enzymes - hyaluronidase, collagenase, lecithinase, neuraminidase, coagulase, proteases. Their characteristics are given in more detail in the lecture on the physiology of microorganisms.

4) Bacterial toxins: exotoxins and endotoxins, nature and properties, mechanisms of action.

The most important pathogenicity factors are considered toxins, which can be divided into two large groups - exotoxins and endotoxins.

Exotoxins are produced into the external environment (host organism), usually of a protein nature, can exhibit enzymatic activity, and can be secreted by both gram-positive and gram-negative bacteria. They have very high toxicity, are thermally unstable, and often exhibit antimetabolite properties. Exotoxins are highly immunogenic and cause the formation of specific neutralizing antibodies - antitoxins. According to the mechanism of action and point of application, exotoxins differ - cytotoxins (enterotoxins and dermatonecrotoxins), membrane toxins (hemolysins, leukocidins), functional blockers (cholerogen), exfoliants and erythrogenins. Microbes capable of producing exotoxins are called Toxigenic.

Endotoxins are released only when bacteria die, are characteristic of gram-negative bacteria, and are complex chemical compounds of the cell wall (LPS) - for more details, see the lecture on the chemical composition of bacteria. Toxicity is determined by lipid A, the toxin is relatively heat stable; immunogenic and toxic properties are less pronounced than those of exotoxins.

The presence of capsules in bacteria complicates the initial stages of protective reactions - recognition and absorption (phagocytosis). A significant factor in invasiveness is the mobility of bacteria, which determines the penetration of microbes into cells and into intercellular spaces.

Pathogenicity factors are controlled:

Chromosome genes;

Plasmid genes;

Genes introduced by temperate phages.