Presentation on the topic of viruses and bacteriophages. Presentation on biology on the topic "Viruses and phages" (grade 10). The structure of bacteriophages. resting, extracellular, form – virion. intracellular form - vegetative. virion

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Lesson plan Viruses, history of the discovery of viruses, their structure. Bacteriophages, their structure. Viral diseases, their prevention. Video fragment “Bacteria and Viruses”. Test tasks to consolidate a new topic.

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THE HISTORY OF THE DISCOVERY OF THE VIRUS Having begun their fight against smallpox and rabies, Jenner and Pasteur did not yet know that they were dealing with completely unusual pathogens, invisible in light microscopes. For the first time, this fact in relation to one of the viruses was accurately established by the Russian botanist Dmitry Ivanovsky in 1892. He was looking for the causative agent of a disease in tobacco, in which the leaves of the plant become spotted - tobacco mosaic. Ivanovsky strained the juice of the diseased plant through a thin porcelain filter that did not allow bacteria to pass through. But this strained juice continued to infect other plants! Later it was proven that the causative agents of other diseases - rabies, foot-and-mouth disease, yellow fever - are also much smaller in size than the smallest bacteria. The newly discovered creatures were called viruses (Latin for “poison”) in 1899 by the Dutch botanist and microbiologist Martin Beijerinck. Viral diseases include influenza, encephalitis, measles, mumps, rubella, hepatitis

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The penetration of the virus into the cell is preceded by its binding to a special receptor protein located on the surface of the cell. The actual reproduction of the virus is expressed in the reduplication of the viral genome with the help of the corresponding enzymes encoded in the genome of the virus. Synthesis of viral proteins and capsid self-assembly. The newly formed viral particles leave the cell and infect other cells.

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Bacteriophages - bacteria eaters A special group is represented by bacterial viruses - bacteriophages, or phages, which are able to penetrate a bacterial cell and destroy it. The body of the E. coli phage consists of a head, from which extends a hollow rod, surrounded by a sheath of contractile protein. The rod ends in a basal plate on which six filaments are attached. Inside the head is DNA. The bacteriophage, with the help of processes, attaches to the surface of E. coli and, at the point of contact with it, dissolves the cell wall with the help of an enzyme. After this, due to contraction of the head, the phage DNA molecule is injected through the rod channel into the cell. After about 10-15 minutes, under the influence of this DNA, the entire metabolism of the bacterial cell is rearranged, and it begins to synthesize the DNA of the bacteriophage, and not its own. At the same time, phage protein is also synthesized. The process ends with the appearance of 200-1,000 new phage particles, as a result of which the bacterial cell dies.

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VIRAL DISEASES Viral diseases. Settling in the cells of living organisms, viruses cause dangerous diseases of many agricultural plants (mosaic disease of tobacco, tomatoes, cucumbers; leaf curl, dwarfism, jaundice, etc.) and domestic animals (foot and mouth disease, plague in swine and birds, infectious anemia in horses, cancer and etc.). These diseases sharply reduce crop yields and lead to mass death of animals. Viruses also cause many dangerous human diseases: influenza, measles, smallpox, polio, mumps, rabies, yellow fever, etc. In recent years, another terrible disease has been added to them - AIDS.

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Rubella Rubella (lat. rubella) or 3rd disease is an epidemic viral disease with an incubation period of about 15-24 days. It is usually a harmless disease that mainly affects children, but it can cause serious birth defects if a woman becomes infected early in pregnancy. The name of the third disease comes from the time when a list of diseases causing childhood rash was compiled, in which it was listed third.

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Chickenpox Chickenpox, chickenpox is an acute viral disease with airborne transmission. Usually characterized by a febrile state, papulovesicular rash with a benign course. The source of infection is a sick person, who poses an epidemic danger from the end of the incubation period until the scabs fall off. The pathogen is spread by airborne droplets. Mostly children aged 6 months to 7 years are affected. Adults rarely get chickenpox, as they usually experience it in childhood.

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Rabies (other names: rabies obsolete hydrophobia, fear of hydrophobia) is an infectious disease caused by the rabies virus. The rabies virus causes specific encephalitis (inflammation of the brain) in animals and humans. It is transmitted through saliva when bitten by a sick animal. Then, spreading along the nerve pathways, the virus reaches the salivary glands and nerve cells of the cerebral cortex and, affecting them, causes severe irreversible damage.

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There is a natural type of rabies, the foci of which are formed by wild animals (wolf, fox, raccoon dog, jackal, arctic fox, skunk, mongoose, bats) and an urban type of rabies (dogs, cats, farm animals). In India, one of the main carriers of rabies are bats (3/4 of human cases of infection from the total rabies incidence statistics). Cases of rabies in small rodents and transmission of the virus from them to humans are practically unknown. There is, however, a hypothesis that the natural reservoir of the virus is rodents, which are able to carry the infection for a long time without dying for several days after infection.

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Periods of the disease The disease has three periods: Prodromal or initial (precursor period) Lasts 1-3 days. Accompanied by an increase in temperature to 37.2-37.3 °C, a depressed state, poor sleep, insomnia, and anxiety of the patient. Pain at the site of the bite is felt even if the wound has healed. High stage (hydrophobia) Lasts 1-4 days. It is expressed in sharply increased sensitivity to the slightest irritation of the sensory organs: bright light, various sounds, noise cause muscle spasms in the limbs. Hydrophobia, aerophobia. Patients become aggressive, violent, hallucinations, delusions, and a feeling of fear appear. Period of paralysis (stage of ominous calm) Paralysis of the eye muscles and lower extremities occurs. Severe paralytic respiratory disorders cause death. The total duration of the disease is 5-8 days, occasionally 10-12 days.

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Diagnostics The presence of a bite or contact with saliva of rabid animals on the damaged skin is of great importance. One of the most important signs of a human disease is hydrophobia with symptoms of spasm of the pharyngeal muscles only at the sight of water and food, which makes it impossible to drink even a glass of water. No less indicative is a symptom of aerophobia - muscle cramps that occur at the slightest movement of air. Increased salivation is also characteristic; in some patients, a thin stream of saliva constantly flows from the corner of the mouth.

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What to do if you are bitten? The first thing to do is to immediately wash the bite area with soap. It is necessary to wash quite intensively, for 10 minutes. There is no need to cauterize the wounds or apply stitches. After this, you need to immediately go to the nearest emergency room, because the success of rabies vaccination greatly depends on how quickly you seek help from a doctor. It is advisable to inform the doctor at the emergency room the following information - a description of the animal, its appearance and behavior, the presence of a collar, the circumstances of the bite. Next, you should undergo a course of vaccinations prescribed by your doctor. And so five or six times. During vaccination and 6 months after it, you must refrain from drinking alcohol. In addition, if you are undergoing a rabies vaccination course, you should not be overtired, hypothermic, or, conversely, overheat. During vaccinations, it is necessary to carefully monitor your health status. And if you have any complaints about worsening your condition, you should consult a doctor.

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Prevention Prevention of rabies consists of combating rabies among animals: vaccination (domestic, stray and wild animals), establishing quarantine, etc. For people bitten by rabid or unknown animals, local treatment of the wound must be carried out immediately or as soon as possible after the bite or injury ; the wound is washed abundantly with soap and water (detergent) and treated with 40-70 degree alcohol or tincture of iodine; if indicated, anti-rabies immunoglobulin is injected deep into the wound and into the soft tissues around it; after local treatment of the wound, specific treatment is immediately carried out, which consists of therapeutic and prophylactic immunization with rabies vaccine.

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AIDS - the plague of the twentieth century AIDS - acquired immunodeficiency syndrome - an epidemic disease that primarily affects the human immune system, which protects it from various pathogens. Damage to the cellular immune system leads to infectious diseases and malignant tumors. The body becomes defenseless to microbes that under normal conditions do not cause illness. The causative agent of the disease is human immunodeficiency virus (HIV). The HIV genome consists of two identical RNA molecules consisting of approximately 10 thousand base pairs. Moreover, HIV isolated from various AIDS patients differs from each other in the number of bases (from 80 to 1,000).

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You can't see him, but he's nearby. HIV has a unique variability, which is five times greater than the variability of the influenza virus and one hundred times greater than that of the hepatitis B virus. Continuous genetic and antigenic variability of the virus in the human population leads to the emergence of new HIV virions, which dramatically complicates the problem of obtaining a vaccine and makes it difficult to administer special AIDS prevention. Moreover, this property of HIV, according to a number of experts, casts doubt on the very fundamental possibility of creating an effective vaccine to protect against AIDS. One of the manifestations of human infection with the AIDS virus is damage to the central nervous system. Typical symptoms specific to AIDS have not been identified.

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What is HIV and AIDS? HIV is the human immunodeficiency virus. It destroys the defense (immune) system, making a person unable to resist infection. People infected with HIV are called “HIV-infected”. AIDS (acquired immunodeficiency syndrome) is a viral infectious disease caused by HIV infection. An infected person (HIV carrier) does not immediately develop AIDS; he looks and feels healthy for 10 years, but he can unintentionally spread the infection. AIDS develops faster in those HIV carriers whose health is weakened by smoking, alcohol, drugs, stress and poor nutrition.

Bacteriophages (from the Latin “phagos” - devouring) are bacterial viruses that have the same characteristic features as other viruses. Characteristic properties of phages, as representatives of the kingdom Vira: phages - non-cellular life forms contain one nucleic acid - DNA or RNA; they lack protein synthesizing systems and independent metabolism; obligate intracellular parasites at the genetic level

Stages of productive infection: 1st stage. Adsorption of phage on a sensitive cell. Occurs in the presence of complementary receptors in the cell wall of bacteria or at the ends of the filaments of the phage process. 2nd stage. Penetration of phage DNA into a bacterial cell. With the help of lysozyme, a section of the cell wall is hydrolyzed, the process sheath contracts and the internal rod pierces the cell membrane. DNA penetrates through the rod channel. 3rd stage. Intracellular development of phage. Bacteriophage DNA directs cellular systems to biosynthesize components necessary for phage reproduction. First, there is the synthesis of “early proteins” - enzymes that carry out DNA replication, and then “late proteins” - proteins of the head, appendage, etc.

4th stage. Phage morphogenesis. Phage maturation is a disconnected process. The phage heads are formed separately: a capsid is built around the DNA. A process is formed independently: a basal plate is formed, an internal rod is attached to it and covered with a sheath. The filaments of the process are synthesized separately. The phage's constituent parts then combine to form virions. 5th stage. Bacterial cell lysis and phage release. Phage lysozyme hydrolyzes the cell wall and causes cell lysis. Bacteriophages are released into the environment.

Integrative infection (lysogeny) prophage DNA phage is included in the circular chromosome of the bacterial cell. During cell division, the prophage (integrated phage DNA) replicates as part of the cellular genome and passes into the next generations of bacteria. A bacterial culture infected with a temperate phage remains viable and becomes lysogenic. Phage conversion: the process of changing the properties of a bacterium, under the influence of an additional set of genes introduced by the prophage into the cell, with the acquisition of toxigenic properties (for example, the appearance of the ability to form an exotoxin in botulism pathogens, diphtheria, scarlet fever).

INDICATION AND ISOLATION OF BACTERIOPHAGE. It is based on the principle of joint inoculation of the material under study and a bacterial culture sensitive to the desired phage - a test culture. Enrichment method with “overseeding”. 1) The test material is suspended and filtered. The filtrate and a homologous test culture are added to a test tube with MPB. Incubate. 2) The contents of the tube are freed from bacteria (centrifugation, filtration). 3) The filtrate is inoculated with the test culture onto MPA plates. Incubate. On the MPA, against the background of the growth of the bacterial culture, round spots appear - negative phage colonies.

Negative phage colonies 4) The material from the spot is transferred to a test tube with MPB, a test culture is added, and incubated. Phages, having multiplied in bacteria, cause their lysis and a phagolysate containing many phages is obtained in a test tube. 5) The phagolysate is completely free of bacteria.

Application of bacteriophages. 1. For the diagnosis of infectious diseases. a) to determine the species of the isolated bacterial culture. b) for phage typing – intraspecific differentiation of a pure bacterial culture. c) for the purpose of indicating the pathogen directly in material from a patient using RSF (rarely used).

Phagotyping Basis of the method Basis of the method: using standard phages, cultures of the same species are differentiated based on their different sensitivity to a set of such phages, that is, the phage type is identified, which makes it possible to identify the source of the disease and the ways of its spread. Phage typing of S. typhi. A set of typical Vi phages (A, B, C, D, E) is used, each of which lyses cultures of specific phages. For typing, the Vi-1 phage is needed, which lyses all typhoid cultures containing Vi-antigen, because only such cultures are suitable for experimentation.

Phage typing of S. typhi. Experiment setup: 1) The broth culture is sown in the form of drops on the surface of the MPA. 2) Typical Vi-phages, as well as phage Vi-1, are applied to dried drops of culture. Incubate. 3) The result of the experiment is taken into account: the culture must be completely lysed by phage Vi-1 and certain standard phages, which allows one to determine its phage type (using the table).

2. For the prevention and treatment of infectious diseases. Antibiotics are widely used to treat infectious diseases, but their improper use causes complications. Bacteriophages are used as an alternative therapy. Bacteriophage preparations are composed of virulent broad-spectrum bacteriophages that are active against antibiotic-resistant bacteria. They are produced liquid and freeze-dried, in the form of tablets, creams, ointments, and suppositories. Before use, it is necessary to determine the phage sensitivity of the infectious agent.

The most commonly used bacteriophage preparations. Coliproteus (a mixture of phagolysates of P.vulgaris and P.mirabilis) Staphylococcal bacteriophage Bacteriophage Pseudomonas aeruginosa Salmonella bacteriophage Polyvalent bacteriophage (a mixture of phagolysates of staphylococci, streptococci, E.coli, P.vulgaris and P.mirabilis)

TITRATION OF BACTERIOPHAGE USING THE GRACE METHOD 1.0 ml of phage is mixed in a test tube with 0.5 ml of bacterial culture and molten MPA is added to the same test tube. All contents are poured into a cup with MPA. Allow the top thin layer to harden and place it in a thermostat. When a phage meets a bacterium, the latter lysis occurs and a negative phage colony is formed. These negative colonies are then counted to determine the titer. The phage titer is the number of phage particles in 1 ml of phage preparation.

PHAGOTYPING OF BACTERIA USING THE FISCHER METHOD The tested daily broth culture is inoculated on the MPA, then the cup is conditionally divided into squares. One drop of different phages is applied to each square. After daily incubation in a thermostat, squares are marked in which bacterial lysis is noted. The phage type of a bacterial culture is determined by the type of phage that lyses it.

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