Sinusitis

Humoral factors of nonspecific defense of the body. Nonspecific and specific body defense factors

Humoral factors that provide resistance to the body include compliment, lysozyme, interferon, properdin, C-reactive protein, normal antibodies, and bactericidin.

Complement is a complex multifunctional system of blood serum proteins that is involved in reactions such as opsonization, stimulation of phagocytosis, cytolysis, neutralization of viruses, and induction of an immune response. There are 9 known fractions of complement, designated C 1 – C 9, which are in the inactive state in the blood serum. Activation of complement occurs under the influence of the antigen-antibody complex and begins with the addition of C 1 1 to this complex. This requires the presence of salts Ca and Mq. The bactericidal activity of complement manifests itself from the earliest stages of fetal life, however, during the neonatal period, complement activity is the lowest compared to other age periods.

Lysozyme is an enzyme from the group of glycosidases. Lysozyme was first described by Fleting in 1922. It is secreted constantly and is detected in all organs and tissues. In the body of animals, lysozyme is found in the blood, tear fluid, saliva, secretions of the mucous membranes of the nose, gastric and duodenal juice, milk, and amniotic fluid of fetuses. Leukocytes are especially rich in lysozyme. The ability of lysozyme to lyse microorganisms is extremely high. It does not lose this property even in a dilution of 1: 1,000,000. Initially, it was believed that lysozyme is active only against gram-positive microorganisms, but it has now been established that against gram-negative bacteria it acts cytolytically together with complement, penetrating through the cell wall damaged by it bacteria to objects of hydrolysis.

Properdin (from Latin perdere - to destroy) is a globulin-type blood serum protein with bactericidal properties. In the presence of compliment and magnesium ions, it exhibits a bactericidal effect against gram-positive and gram-negative microorganisms, and is also capable of inactivating influenza and herpes viruses, and is bactericidal against many pathogenic and opportunistic microorganisms. The level of properdin in the blood of animals reflects the state of their resistance and sensitivity to infectious diseases. A decrease in its content was revealed in irradiated animals, patients with tuberculosis, and with streptococcal infection.

C-reactive protein - like immunoglobulins, has the ability to initiate reactions of precipitation, agglutination, phagocytosis, and complement fixation. In addition, C-reactive protein increases the mobility of leukocytes, which suggests its participation in the formation of nonspecific resistance of the body.

C-reactive protein is found in blood serum during acute inflammatory processes, and it can serve as an indicator of the activity of these processes. This protein is not detected in normal blood serum. It does not pass through the placenta.

Normal antibodies are almost always present in the blood serum and are constantly involved in nonspecific protection. They are formed in the body as a normal component of serum as a result of contact of the animal with a very large number of different environmental microorganisms or certain dietary proteins.

Bactericidin is an enzyme that, unlike lysozyme, acts on intracellular substances.

Nonspecific protective factors are understood as innate internal mechanisms for maintaining the genetic constancy of the body, which have a wide range of antimicrobial effects. It is nonspecific mechanisms that act as the first protective barrier to the introduction of an infectious agent. Nonspecific mechanisms do not require restructuring, while specific agents (antibodies, sensitized lymphocytes) appear after a few days. It is important to note that nonspecific defense factors act against many pathogenic agents simultaneously.

Leather. Intact skin is a powerful barrier to the penetration of microorganisms. In this case, mechanical factors are important: rejection of the epithelium and secretions of the sebaceous and sweat glands, which have bactericidal properties (chemical factor).

Mucous membranes. In various organs they are one of the barriers to the penetration of microbes. In the respiratory tract, mechanical protection is provided by ciliated epithelium. The movement of the cilia of the epithelium of the upper respiratory tract constantly moves the mucus film along with microorganisms towards the natural openings: the oral cavity and nasal passages. Coughing and sneezing help remove germs. The mucous membranes secrete secretions that have bactericidal properties, in particular due to lysozyme and immunoglobulin type A.

The secretions of the digestive tract, along with their special properties, have the ability to neutralize many pathogenic microbes. Saliva is the first secretion that processes food substances, as well as microflora entering the oral cavity. In addition to lysozyme, saliva contains enzymes (amylase, phosphatase, etc.). Gastric juice also has a detrimental effect on many pathogenic microbes (the causative agents of tuberculosis and anthrax bacillus survive). Bile causes the death of pasteurella, but is ineffective against salmonella and E. coli.

There are billions of different microorganisms in the animal's intestines, but its mucous membrane contains powerful antimicrobial factors, as a result of which infection through it is rare. Normal intestinal microflora has pronounced antagonistic properties towards many pathogenic and putrefactive microorganisms.

Lymph nodes. If microorganisms overcome the skin and mucous barriers, the lymph nodes begin to perform a protective function. Inflammation develops in them and in the infected area of tissue - the most important adaptive reaction aimed at limiting the effect of damaging factors. In the area of inflammation, microbes are fixed by the fibrin filaments formed. In addition to the coagulation and fibrinolytic systems, the inflammatory process involves the complement system, as well as endogenous mediators (prostaglandids, vasoactive amines, etc.). Inflammation is accompanied by fever, swelling, redness and pain. Subsequently, phagocytosis (cellular defense factors) takes an active part in freeing the body from microbes and other foreign factors.

Phagocytosis (from the Greek phago - eat, cytos - cell) is the process of active absorption by the cells of the body of pathogenic living or dead microbes and other foreign particles entering it, followed by digestion with the help of intracellular enzymes. In lower unicellular and multicellular organisms, the process of nutrition is carried out using phagocytosis. In higher organisms, phagocytosis has acquired the property of a protective reaction, liberating the body from foreign substances, both coming from outside and those formed directly in the body itself. Consequently, phagocytosis is not only a reaction of cells to the introduction of pathogenic microbes - it is a more general biological reaction of cellular elements, which is observed in both pathological and physiological conditions.

Types of phagocytic cells. Phagocytic cells are usually divided into two main categories: microphages (or polymorphonuclear phagocytes - PMN) and macrophages (or mononuclear phagocytes - MN). The vast majority of phagocytic PMNs are neutrophils. Among macrophages, a distinction is made between mobile (circulating) and immobile (sedentary) cells. Mobile macrophages are monocytes of peripheral blood, and immobile macrophages are macrophages of the liver, spleen, lymph nodes, lining the walls of small vessels and other organs and tissues.

One of the main functional elements of macro- and microphages are lysosomes - granules with a diameter of 0.25-0.5 microns, containing a large set of enzymes (acid phosphatase, B-glucuronidase, myeloperoxidase, collagenase, lysozyme, etc.) and a number of other substances (cationic proteins, phagocytin, lactoferrin) capable of participating in the destruction of various antigens.

Phases of the phagocytic process. The process of phagocytosis includes the following stages: 1) chemotaxis and adhesion of particles to the surface of phagocytes; 2) gradual immersion (capture) of particles into the cell, followed by separation of part of the cell membrane and the formation of a phagosome; 3) fusion of the phagosome with lysosomes; 4) enzymatic digestion of captured particles and removal of remaining microbial elements. The activity of phagocytosis is associated with the presence of opsonins in the blood serum. Opsonins are proteins in normal blood serum that combine with microbes, making the latter more accessible to phagocytosis. There are thermostable and thermolabile opsonins. The former mainly belong to immunoglobulin G, although opsonins related to immunoglobulins A and M can promote phagocytosis. Thermolabile opsonins (destroyed at a temperature of 56 ° C for 20 minutes) include components of the complement system - C1, C2, C3 and C4.

Phagocytosis, in which the death of the phagocytosed microbe occurs, is called completed (perfect). However, in some cases, microbes located inside phagocytes do not die, and sometimes even multiply (for example, the causative agent of tuberculosis, anthrax bacillus, some viruses and fungi). Such phagocytosis is called incomplete (imperfect). It should be noted that macrophages, in addition to phagocytosis, perform regulatory and effector functions, cooperatively interacting with lymphocytes during a specific immune response.

Humoral factors. Humoral factors of nonspecific defense of the body include: normal (natural) antibodies, lysozyme, properdin, beta-lysines (lysines), complement, interferon, viral inhibitors in the blood serum and a number of other substances that are constantly present in the body.

Normal antibodies. In the blood of animals and humans that have never been sick or been immunized before, substances are found that react with many antigens, but in low titers, not exceeding a dilution of 1:10-1:40. These substances were called normal or natural antibodies. They are believed to arise as a result of natural immunization by various microorganisms.

Lysozyme. Lysozyme belongs to lysosomal enzymes, found in tears, saliva, nasal mucus, secretions of mucous membranes, blood serum and extracts of organs and tissues, milk, and there is a lot of lysozyme in the whites of chicken eggs. Lysozyme is resistant to heat (inactivated by boiling) and has the property of lysing living and dead, mainly gram-positive, microorganisms.

Secretory immunoglobulin A. It has been found that SIgA is constantly present in the contents of the secretions of the mucous membranes, in the secretions of the mammary and salivary glands, in the intestinal tract, and has pronounced antimicrobial and antiviral properties.

Properdin (Latin pro and perdere - prepare for destruction). Described in 1954 by Pillimer as a factor of nonspecific protection and cytolysis. Contained in normal blood serum in amounts up to 25 mcg/ml. This is whey protein with a mol. weighing 220,000. Properdin takes part in the destruction of microbial cells, neutralization of viruses, and lysis of some red blood cells. It is generally accepted that activity is due not to properdin itself, but to the properdin system (complement and divalent magnesium ions). Native properdin plays a significant role in nonspecific activation of complement (alternative pathway of complement activation).

Lysines are blood serum proteins that have the ability to lyse certain bacteria or red blood cells. The blood serum of many animals contains beta-lysines, which cause lysis of Bacillus subtilis and are also very active against many pathogenic microbes.

Lactoferrin. Lactoferrin is a non-hymine glycoprotein with iron-binding activity. Binds two ferric iron atoms to compete with microbes, resulting in microbial growth being inhibited. It is synthesized by polymorphonuclear leukocytes and grape-shaped cells of the glandular epithelium. It is a specific component of the secretion of glands - salivary, lacrimal, mammary, respiratory, digestive and genitourinary tracts. It is generally accepted that lactoferrin is a factor of local immunity that protects epithelial integuments from microbes.

Complement. Complement is a multicomponent system of proteins in blood serum and other body fluids that play an important role in maintaining immune homeostasis. It was first described by Buchner in 1889 under the name “alexin” - a thermolabile factor, in the presence of which lysis of microbes is observed. The term “complement” was introduced by Ehrlich in 1895. It has long been noted that specific antibodies in the presence of fresh blood serum can cause hemolysis of red blood cells or lysis of a bacterial cell, but if the serum is heated at 56 ° C for 30 minutes before the reaction, then lysis won't happen. It turned out that hemolysis (lysis) occurs due to the presence of complement in fresh serum. The largest amount of complement is found in the blood serum of guinea pigs.

The complement system consists of at least 11 different serum proteins, designated C1 to C9. C1 has three subunits: Clq, Clr, C Is. The activated form of complement is indicated by a dash above (C).

There are two ways of activation (self-assembly) of the complement system - classical and alternative, differing in trigger mechanisms.

In the classical activation pathway, the first complement component C1 binds to immune complexes (antigen + antibody), which include sequential subcomponents (Clq, Clr, Cls), C4, C2 and C3. The complex of C4, C2 and C3 ensures the fixation of the activated C5 complement component on the cell membrane, and is then activated through a series of reactions of C6 and C7, which contribute to the fixation of C8 and C9. As a result, damage to the cell wall or lysis of the bacterial cell occurs.

In the alternative pathway of complement activation, the activators themselves are the viruses, bacteria or exotoxins themselves. The alternative activation pathway does not involve components C1, C4 and C2. Activation begins at the S3 stage, which includes a group of proteins: P (properdin), B (proactivator), D (S3 proactivator convertase) and inhibitors J and H. In the reaction, Properdin stabilizes convertases S3 and C5, therefore this activation pathway is also called the properdin system . The reaction begins with the addition of factor B to S3; as a result of a series of sequential reactions, P (properdin) is inserted into the complex (S3 convertase), which acts as an enzyme on S3 and C5; a cascade of complement activation begins with C6, C7, C8 and C9, which leads to to cell wall damage or cell lysis.

Thus, for the body, the complement system serves as an effective defense mechanism, which is activated as a result of immune reactions or through direct contact with microbes or toxins. Let us note some biological functions of activated complement components: Clq is involved in regulating the process of switching immunological reactions from cellular to humoral and vice versa; Cell-bound C4 promotes immune attachment; S3 and C4 enhance phagocytosis; C1/C4, by binding to the surface of the virus, block the receptors responsible for the introduction of the virus into the cell; C3 and C5a are identical to anaphylactosins; they act on neutrophil granulocytes, the latter secrete lysosomal enzymes that destroy foreign antigens, provide directed migration of microphages, cause contraction of smooth muscles, and increase inflammation (Fig. 13).

It has been established that macrophages synthesize C1, C2, C4, C3 and C5. Hepatocytes - C3, C6, C8 cells.

Interferon, Isolated in 1957 by English virologists A. Isaac and I. Lindenman. Interferon was initially considered as an antiviral defense factor. Later it turned out that this is a group of protein substances whose function is to ensure the genetic homeostasis of the cell. In addition to viruses, inducers of the formation of interferon are bacteria, bacterial toxins, mitogens, etc. Depending on the cellular origin of interferon and the factors inducing its synthesis, there are interferon, or leukocyte, which is produced by leukocytes treated with viruses and other agents, interferon, or fibroblast, which produced by fibroblasts treated with viruses or other agents. Both of these interferons are classified as type I. Immune interferon, or γ-interferon, is produced by lymphocytes and macrophages activated by non-viral inducers.

Interferon takes part in the regulation of various mechanisms of the immune response: it enhances the cytotoxic effect of sensitized lymphocytes and K-cells, has antiproliferative and antitumor effects, etc. Interferon has tissue specificity, i.e. it is more active in the biological system in which it is produced, protects cells from a viral infection only if it interacts with them before contact with the virus.

The process of interaction of interferon with sensitive cells is divided into several stages: 1) adsorption of interferon on cellular receptors; 2) induction of an antiviral state; 3) development of antiviral resistance (accumulation of interferon-induced RNA and proteins); 4) pronounced resistance to viral infection. Consequently, interferon does not interact directly with the virus, but prevents the penetration of the virus and inhibits the synthesis of viral proteins on cellular ribosomes during the replication of viral nucleic acids. Interferon has also been shown to have radiation protective properties.

Serum inhibitors. Inhibitors are nonspecific antiviral substances of protein nature, contained in normal native blood serum, secretions of the epithelium of the mucous membranes of the respiratory and digestive tracts, and in extracts of organs and tissues. They have the ability to suppress the activity of viruses outside the sensitive cell, when the virus is in the blood and liquids. Inhibitors are divided into thermolabile (lose their activity when blood serum is heated at 60-62 °C for 1 hour) and thermostable (withstand heating up to 100 °C). Inhibitors have universal virus neutralizing and antihemagglutinating activity against many viruses.

In addition to serum inhibitors, inhibitors of tissues, secretions and animal excreta have been described. Such inhibitors have proven to be active against many viruses; for example, secretory inhibitors of the respiratory tract have antihemagglutinating and virus-neutralizing activity.

Bactericidal activity of blood serum (BAS). Fresh blood serum of humans and animals has pronounced, mainly bacteriostatic, properties against many pathogens of infectious diseases. The main components that suppress the growth and development of microorganisms are normal antibodies, lysozyme, properdin, complement, monokines, leukins and other substances. Therefore, BAS is an integrated expression of the antimicrobial properties that are part of the humoral factors of nonspecific defense. BAS depends on the conditions of keeping and feeding of animals; with poor housing and feeding, the activity of the serum is significantly reduced.

The meaning of stress. Nonspecific protective factors also include protective-adaptive mechanisms, called “stress,” and factors that cause stress are called stressors by G. Silje. According to Silye, stress is a special nonspecific state of the body that occurs in response to the action of various damaging environmental factors (stressors). In addition to pathogenic microorganisms and their toxins, stressors can be cold, heat, hunger, ionizing radiation and other agents that have the ability to cause responses in the body. Adaptation syndrome can be general and local. It is caused by the action of the pituitary-adrenocortical system associated with the hypothalamic center. Under the influence of a stressor, the pituitary gland begins to intensively secrete adrenocorticotropic hormone (ACTH), which stimulates the functions of the adrenal glands, causing them to increase the release of an anti-inflammatory hormone such as cortisone, which reduces the protective-inflammatory response. If the stressor is too strong or prolonged, then a disease occurs during the adaptation process.

With the intensification of livestock farming, the number of stress factors to which animals are exposed increases significantly. Therefore, the prevention of stress effects that reduce the body’s natural resistance and cause diseases is one of the most important tasks of the veterinary and zootechnical service.

Humoral factors that provide resistance to the body include compliment, lysozyme, interferon, properdin, C-reactive protein, normal antibodies, and bactericidin.

Bactericidin is an enzyme that, unlike lysozyme, acts on intracellular substances.

humoral factors - complement system. Complement is a complex of 26 proteins in the blood serum. Each protein is designated as a fraction in Latin letters: C4, C2, C3, etc. Under normal conditions, the complement system is in an inactive state. When antigens enter, it is activated; the stimulating factor is the antigen-antibody complex. Any infectious inflammation begins with the activation of complement. The complement protein complex is integrated into the cell membrane of the microbe, which leads to cell lysis. Complement is also involved in anaphylaxis and phagocytosis, as it has chemotactic activity. Thus, complement is a component of many immunolytic reactions aimed at freeing the body from microbes and other foreign agents;

AIDS

The discovery of HIV was preceded by the work of R. Gallo and his colleagues, who isolated two human T-lymphotropic retroviruses using the T-lymphocyte cell culture they obtained. One of them, HTLV-I (humen T-lymphotropic virus type I), discovered in the late 70s, is the causative agent of a rare but malignant human T-leukemia. A second virus, designated HTLV-II, also causes T-cell leukemias and lymphomas.

After registering the first patients with acquired immunodeficiency syndrome (AIDS), a then unknown disease, in the United States in the early 80s, R. Gallo suggested that its causative agent was a retrovirus close to HTLV-I. Although this assumption was refuted a few years later, it played a large role in the discovery of the true causative agent of AIDS. In 1983, from a piece of tissue from an enlarged lymph node of a homosexual, Luc Montenier and a group of employees at the Pasteur Institute in Paris isolated a retrovirus in a culture of T-helper cells. Further studies showed that this virus was different from HTLV-I and HTLV-II - it reproduced only in T helper and effector cells, designated T4, and did not reproduce in T suppressor and killer cells, designated T8.

Thus, the introduction of T4 and T8 lymphocyte cultures into virological practice made it possible to isolate three obligate lymphotropic viruses, two of which caused the proliferation of T-lymphocytes, expressed in various forms of human leukemia, and one, the causative agent of AIDS, caused their destruction. The latter is called the human immunodeficiency virus - HIV.

Structure and chemical composition. HIV virions are spherical, 100-120 nm in diameter, and are similar in structure to other lentiviruses. The outer shell of virions is formed by a lipid bilayer with glycoprotein “spikes” located on it (Fig. 21.4). Each “spike” consists of two subunits (gp41 and gp!20). The first penetrates the lipid layer, the second is located outside. The lipid layer originates from the outer membrane of the host cell. The formation of both proteins (gp41 and gp!20) with a non-covalent bond between them occurs when the HIV outer shell protein (gp!60) is cut. Under the outer shell there is a cylindrical or cone-shaped core of the virion, formed by proteins (p!8 and p24). The core contains RNA, reverse transcriptase and internal proteins (p7 and p9).

Unlike other retroviruses, HIV has a complex genome due to the presence of a system of regulatory genes. Without knowledge of the basic mechanisms of their functioning, it is impossible to understand the unique properties of this virus, manifested in the various pathological changes that it causes in the human body.

The HIV genome contains 9 genes. Three structural genes gag, pol And env encode components of viral particles: gene gag- internal proteins of the virion, which are part of the core and capsid; gene pol- reverse transcriptase; gene env- type-specific proteins found in the outer shell (glycoproteins gp41 and gp!20). The large molecular weight of gp!20 is due to their high degree of glycosylation, which is one of the reasons for the antigenic variability of this virus.

Unlike all known retroviruses, HIV has a complex system of regulation of structural genes (Fig. 21.5). Among them, genes attract the most attention tat And rev. Gene product tat increases the rate of transcription of both structural and regulatory viral proteins tens of times. Gene product rev is also a transcription regulator. However, it controls the transcription of either regulatory or structural genes. As a result of this transcription switch, capsid proteins are synthesized instead of regulatory proteins, which increases the rate of virus reproduction. Thus, with the participation of the gene rev the transition from latent infection to its active clinical manifestation may be determined. Gene nef controls the cessation of HIV reproduction and its transition to a latent state, and the gene vif encodes a small protein that enhances the virion's ability to bud from one cell and infect another. However, this situation will become even more complicated when the mechanism of regulation of proviral DNA replication by gene products is finally elucidated vpr And vpu. At the same time, at both ends of the DNA of the provirus, integrated into the cellular genome, there are specific markers - long terminal repeats (LTRs), consisting of identical nucleotides, which are involved in the regulation of the expression of the genes considered. At the same time, there is a certain algorithm for the inclusion of genes during the process of viral reproduction in different phases of the disease.

Antigens. Core proteins and envelope glycoproteins (gp!60) have antigenic properties. The latter are characterized by a high level of antigenic variability, which is determined by the high rate of nucleotide substitutions in genes env And gag, hundreds of times higher than the corresponding figure for other viruses. During the genetic analysis of numerous HIV isolates, there was not a single one with a complete match of nucleotide sequences. Deeper differences were noted in HIV strains isolated from patients living in different geographic areas (geographical variants).

However, HIV variants have common antigenic epitopes. Intense antigenic variability of HIV occurs in the body of patients during infection and virus carriers. It allows the virus to “hide” from specific antibodies and cellular immunity factors, which leads to chronic infection.

The increased antigenic variability of HIV significantly limits the possibilities of creating a vaccine to prevent AIDS.

Currently, two types of pathogens are known - HIV-1 and HIV-2, which differ in antigenic, pathogenic and other properties. Initially, HIV-1 was isolated, which is the main causative agent of AIDS in Europe and America, and a few years later in Senegal, HIV-2 was isolated, which is distributed mainly in West and Central Africa, although isolated cases of the disease are also found in Europe.

In the United States, live adenovirus vaccine is successfully used to immunize military personnel.

Laboratory diagnostics. To detect viral antigen in the epithelial cells of the mucous membrane of the respiratory tract, immunofluorescent and immunoenzyme methods are used, and in feces, immunoelectron microscopy is used. Isolation of adenoviruses is carried out by infecting sensitive cell cultures, followed by identification of the virus in RNA, and then in the neutralization reaction and RTGA.

Serodiagnosis is carried out in the same reactions with paired sera of sick people.

Ticket 38

Culture media

Microbiological research is the isolation of pure cultures of microorganisms, cultivation and study of their properties. Cultures consisting of microorganisms of the same type are called pure. They are needed in the diagnosis of infectious diseases, to determine the species and type of microbes, in research work, to obtain waste products of microbes (toxins, antibiotics, vaccines, etc.).

For the cultivation of microorganisms (cultivation under artificial conditions in vitro), special substrates are required - nutrient media. On media, microorganisms carry out all life processes (eat, breathe, reproduce, etc.), which is why they are also called “culture media.”

Culture media

Culture media are the basis of microbiological work, and their quality often determines the results of the entire study. Environments must create optimal (best) conditions for the life of microbes.

Environment requirements

Environments must meet the following conditions:

1) be nutritious, i.e. contain in an easily digestible form all the substances necessary to meet nutritional and energy needs. They are sources of organogens and mineral (inorganic) substances, including trace elements. Mineral substances not only enter the cell structure and activate enzymes, but also determine the physicochemical properties of media (osmotic pressure, pH, etc.). When cultivating a number of microorganisms, growth factors are added to the media - vitamins, some amino acids that the cell cannot synthesize;

Attention! Microorganisms, like all living things, need plenty of water.

2) have an optimal concentration of hydrogen ions - pH, since only with an optimal reaction of the environment, affecting the permeability of the shell, can microorganisms absorb nutrients.

For most pathogenic bacteria, a slightly alkaline environment (pH 7.2-7.4) is optimal. The exception is Vibrio cholerae - its optimum is in the alkaline zone

(pH 8.5-9.0) and the causative agent of tuberculosis, which requires a slightly acidic reaction (pH 6.2-6.8).

To prevent acidic or alkaline products of their vital activity from changing the pH during the growth of microorganisms, the media must be buffered, i.e., contain substances that neutralize metabolic products;

3) be isotonic for the microbial cell, that is, the osmotic pressure in the medium must be the same as inside the cell. For most microorganisms, the optimal environment is a 0.5% sodium chloride solution;

4) be sterile, since foreign microbes interfere with the growth of the microbe under study, the determination of its properties and change the properties of the medium (composition, pH, etc.);

5) solid media must be moist and have an optimal consistency for microorganisms;

6) have a certain redox potential, i.e. the ratio of substances donating and accepting electrons, expressed by the RH2 index. This potential shows the saturation of the environment with oxygen. Some microorganisms require a high potential, while others require a low one. For example, anaerobes reproduce at RH2 no higher than 5, and aerobes at RH2 no lower than 10. The redox potential of most environments satisfies the requirements of aerobes and facultative anaerobes;

7) be as unified as possible, i.e. contain constant amounts of individual ingredients. Thus, media for the cultivation of most pathogenic bacteria should contain 0.8-1.2 g of amino nitrogen NH2, i.e., the total nitrogen of the amino groups of amino acids and lower polypeptides; 2.5-3.0 hl total nitrogen N; 0.5% chlorides in terms of sodium chloride; 1% peptone.

It is desirable that the media be transparent - it is more convenient to monitor the growth of crops, and it is easier to notice contamination of the environment with foreign microorganisms.

Classification of media

The need for nutrients and environmental properties varies among different types of microorganisms. This eliminates the possibility of creating a universal environment. In addition, the choice of a particular environment is influenced by the objectives of the study.

Currently, a huge number of environments have been proposed, the classification of which is based on the following characteristics.

1. Initial components. Based on the starting components, natural and synthetic media are distinguished. Natural media are prepared from animal products and

of plant origin. Currently, media have been developed in which valuable food products (meat, etc.) are replaced with non-food ones: bone and fish meal, feed yeast, blood clots, etc. Despite the fact that the composition of nutrient media from natural products is very complex and varies depending from raw materials, these media are widely used.

Synthetic media are prepared from certain chemically pure organic and inorganic compounds, taken in precisely specified concentrations and dissolved in double-distilled water. An important advantage of these media is that their composition is constant (it is known how much and what substances they contain), so these media are easily reproducible.

2. Consistency (degree of density). Media are liquid, dense and semi-liquid. Solid and semi-liquid media are prepared from liquid substances, to which agar-agar or gelatin is usually added to obtain a medium of the desired consistency.

Agar-agar is a polysaccharide obtained from certain

varieties of seaweed. It is not a nutrient for microorganisms and serves only to compact the environment. In water, agar melts at 80-100°C and solidifies at 40-45°C.

Gelatin is an animal protein. Gelatin media melt at 25-30°C, so crops are usually grown on them at room temperature. The density of these media decreases at a pH below 6.0 and above 7.0, and they harden poorly. Some microorganisms use gelatin as a nutrient - as they grow, the medium liquefies.

In addition, clotted blood serum, coagulated eggs, potatoes, and media with silica gel are used as solid media.

3. Composition. Environments are divided into simple and complex. The first include meat peptone broth (MPB), meat peptone agar (MPA), Hottinger broth and agar, nutritious gelatin and peptone water. Complex media are prepared by adding to simple media blood, serum, carbohydrates and other substances necessary for the reproduction of a particular microorganism.

4. Purpose: a) basic (commonly used) media are used for cultivating most pathogenic microbes. These are the above-mentioned MP A, MPB, broth and Hottinger agar, peptone water;

b) special media are used for isolating and growing microorganisms that do not grow on simple media. For example, for the cultivation of streptococcus, sugar is added to the media, for pneumo- and meningococci - blood serum, for the causative agent of whooping cough - blood;

c) elective (selective) environments serve to isolate a certain type of microbes, the growth of which they favor, delaying or suppressing the growth of accompanying microorganisms. Thus, bile salts, suppressing the growth of E. coli, make the environment

selective for the causative agent of typhoid fever. Media become selective when certain antibiotics, salts are added to them, and pH changes.

Liquid elective media are called accumulation media. An example of such a medium is peptone water with a pH of 8.0. At this pH, Vibrio cholerae actively multiplies on it, and other microorganisms do not grow;

d) differential diagnostic media make it possible to distinguish (differentiate) one type of microbe from another by enzymatic activity, for example, Hiss media with carbohydrates and an indicator. With the growth of microorganisms that break down carbohydrates, the color of the medium changes;

e) preservative media are intended for primary seeding and transportation of the test material; they prevent the death of pathogenic microorganisms and suppress the development of saprophytes. An example of such a medium is a glycerol mixture used to collect stool in studies conducted to detect a range of intestinal bacteria.

Hepatitis (A,E)

The causative agent of hepatitis A (HAV-Hepatitis A virus) belongs to the picornavirus family, the genus of enteroviruses. Causes the most common viral hepatitis, which has several historical names (infectious, epidemic hepatitis, Botkin's disease, etc.). In our country, about 70% of cases of viral hepatitis are caused by the hepatitis A virus. The virus was first discovered by S. Feystone in 1979 in the feces of patients using immune electron microscopy.

Structure and chemical composition. In terms of morphology and structure, the hepatitis A virus is close to all enteroviruses (see 21.1.1.1). The RNA of the hepatitis A virus contains nucleotide sequences common to other enteroviruses.

The hepatitis A virus has one virus-specific antigen of a protein nature. HAV differs from enteroviruses in its higher resistance to physical and chemical factors. It is partially inactivated when heated to 60°C for 1 hour, at 100°C it is destroyed within 5 minutes, and is sensitive to the action of formalin and UV radiation.

Cultivation and reproduction. The hepatitis virus has a reduced ability to reproduce in cell cultures. However, it was possible to adapt it to continuous cell lines of humans and monkeys. Reproduction of the virus in cell culture is not accompanied by CPE. HAV is almost not detected in the culture fluid, since it is associated with cells in the cytoplasm of which it reproduces:

Pathogenesis of human diseases and immunity. HAV, like other enteroviruses, enters the gastrointestinal tract with food, where it reproduces in the epithelial cells of the mucous membrane of the small intestine and regional lymph nodes. The pathogen then enters the blood, in which it is detected at the end of the incubation period and in the first days of the disease.

Unlike other enteroviruses, the main target of the damaging effect of HAV are liver cells, in the cytoplasm of which its reproduction occurs. It is possible that hepatocytes are damaged by NK cells (natural killer cells), which in an activated state can interact with them, causing their destruction. Activation of NK cells also occurs as a result of their interaction with interferon induced by the virus. Damage to hepatocytes is accompanied by the development of jaundice and an increase in the level of transaminases in the blood serum. Next, the pathogen enters the intestinal lumen with bile and is excreted in feces, which contain a high concentration of the virus at the end of the incubation period and in the first days of the disease (before the development of jaundice). Hepatitis A usually ends with complete recovery, and deaths are rare.

After suffering a clinically pronounced or asymptomatic infection, lifelong humoral immunity is formed, associated with the synthesis of antiviral antibodies. Immunoglobulins of the IgM class disappear from the serum 3-4 months after the onset of the disease, while IgG persists for many years. The synthesis of secretory immunoglobulins SlgA has also been established.

Epidemiology. The source of infection is sick people, including those with a common asymptomatic form of infection. The hepatitis A virus circulates widely among the population. On the European continent, serum antibodies against HAV are found in 80% of the adult population over 40 years of age. In countries with low socioeconomic levels, infection occurs already in the first years of life. Hepatitis A often affects children.

The patient is most dangerous to others at the end of the incubation period and in the first days of the height of the disease (before the appearance of jaundice) due to the maximum release of the virus in feces. The main mechanism of transmission is fecal-oral - through food, water, household items, children's toys.

Laboratory diagnosis is carried out by identifying the virus in the patient’s feces using immunoelectron microscopy. Viral antigen in feces can also be detected using enzyme immunoassay and radioimmunoassay. The most widely used serodiagnosis of hepatitis is the detection, using the same methods, of IgM class antibodies in paired blood sera, which reach a high titer during the first 3-6 weeks.

Specific prevention. Vaccine prevention of hepatitis A is under development. Inactivated and live culture vaccines are being tested, the production of which is difficult due to the weak reproduction of the virus in cell cultures. The most promising is the development of a genetically engineered vaccine. For passive immunoprophylaxis of hepatitis A, immunoglobulin obtained from a mixture of donor sera is used.

The causative agent of hepatitis E has some similarities with caliciviruses. The size of the viral particle is 32-34 nm. The genetic material is represented by RNA. Transmission of the hepatitis E virus, like HAV, occurs through the enteral route. Serodiagnosis is carried out by determining antibodies to the E-virus antigen.

Phagocytosis

The process of phagocytosis is the absorption of a foreign substance by phagocyte cells. Reticular and endothelial cells of lymph nodes, spleen, bone marrow, Kupffer cells of the liver, histiocytes, monocytes, polyblasts, neutrophils, eosinophils, basophils have phagocytic activity. Phagocytes remove dying cells from the body, absorb and inactivate microbes, viruses, and fungi; synthesize biologically active substances (lysozyme, complement, interferon); participate in the regulation of the immune system.

The mechanism of phagocytosis includes the following steps:

1) activation of the phagocyte and its approach to the object (chemotaxis);

2) adhesion stage - adherence of the phagocyte to the object;

3) absorption of an object with the formation of a phagosome;

4) formation of a phagolysosome and digestion of the object using enzymes.

The activity of phagocytosis is associated with the presence of opsonins in the blood serum. Opsonins are proteins in normal blood serum that combine with microbes, making them more accessible to phagocytosis.

Phagocytosis, in which the death of the phagocytosed microbe occurs, is called complete. However, in some cases, microbes located inside phagocytes do not die, and sometimes even multiply. This type of phagocytosis is called incomplete. Macrophages, in addition to phagocytosis, perform regulatory and effector functions, cooperatively interacting with lymphocytes during a specific immune response.

defense organism antimicrobial phagocytosis

Humoral factors of nonspecific protection

The main humoral factors of nonspecific defense of the body include lysozyme, interferon, complement system, properdin, lysines, lactoferrin.

Lysozyme is a lysosomal enzyme and is found in tears, saliva, nasal mucus, secretions of mucous membranes, and blood serum. It has the property of lysing living and dead microorganisms.

Interferons are proteins that have antiviral, antitumor, and immunomodulatory effects. Interferon acts by regulating the synthesis of nucleic acids and proteins, activating the synthesis of enzymes and inhibitors that block the translation of viral and RNA.

Nonspecific humoral factors include the complement system (a complex protein complex that is constantly present in the blood and is an important factor in immunity). The complement system consists of 20 interacting protein components that can be activated without the participation of antibodies, forming a membrane attack complex with subsequent attack on the membrane of a foreign bacterial cell, leading to its destruction. The cytotoxic function of complement in this case is activated directly by the foreign invading microorganism.

Properdin takes part in the destruction of microbial cells, neutralization of viruses and plays a significant role in the nonspecific activation of complement.

Lysines are blood serum proteins that have the ability to lyse certain bacteria.

Lactoferrin is a local immunity factor that protects epithelial surfaces from microbes.