Genetic material of Shigella, the causative agent of dysentery. Shigella - the causative agent of bacterial dysentery

Shigella The causative agents of dysentery (shigellosis) are several species of bacteria united in the genus Shigella. One of them was first discovered in 1891 by the Russian doctor A. Grigoriev and studied during the epidemic in Japan in 1898 by Shiga. Subsequently, other species of Shigella were isolated and described. According to the modern classification, the genus Shigella includes 4 groups, respectively 4 species. All species, except S. sonnei, are divided into serovars, S. flexneri - also into subserovars (Table 8). In recent decades, dysentery is most often caused by Shigella Flexner and Sonne, and less commonly by Shigella Boyd. S. dysenteriae (Grigorieva-Shiga) is not found in Russia. Shigella are short gram-negative rods; they do not form spores or capsules; unlike salmonella, they do not have flagella. Facultative anaerobes. They grow on simple nutrient media, optimum temperature 37°C, pH 6.8-7.2. They differ in biochemical properties (Table 5). Glucose is fermented, lactose is not fermented on the first day (Shigella Sonne - after a few days), mannitol is fermented by all species except S. dysenteriae. Antigens. Shigella contains O-antigens, some serovars have a K-antigen. Among O-antigens there are specific and group ones. Toxin formation. An exotoxin with a neurotropic effect is produced by S. dysenteriae, and this species causes the disease in the most severe form. All Shigella contain heat-stable endotoxin. Sustainability. S. sonnei is the most resistant in the external environment. Boiling kills Shigella immediately; at 60°C they die after 10-20 minutes, but there are heat-resistant S. sonnei that die only at 70°C for 10 minutes, that is, they can survive pasteurization of milk. In water, soil, food, on objects, in dishes, Shigella remains viable for one to two weeks. S. sonnei can reproduce in milk. Shigella survives in the intestines of flies and on their legs for 2-3 days. By flying from sewage and waste to food products, flies can transmit pathogens. At the same time, Shigella is very unstable in fecal samples, as they die under the influence of antagonistic microbes and the acidic reaction of the environment. Therefore, samples taken for research must be immediately inoculated on a nutrient medium. Disease in humans. The source of infection is a human patient or carrier. The transmission mechanism is fecal-oral. Infection occurs through the mouth. The incubation period lasts from 2 to 7 days. The pathogen penetrates the epithelial cells of the colon mucosa and multiplies in them. This leads to inflammation (colitis) and the formation of ulcers. Main symptoms: increased body temperature, pain in the lower abdomen, vomiting, frequent bowel movements, in severe cases, a mixture of mucus and blood in the stool; a characteristic symptom is tenesmus (false painful urges). The disease lasts 8-10 days. Patients with mild forms of the disease often do not seek qualified help and self-medicate. Untreated dysentery can become chronic. Immunity. After an illness, immunity is not stable. During the disease, antibodies are formed, the detection of which has diagnostic value. Laboratory diagnostics. The material for bacteriological research is excrement (faeces). The sample should be taken before the start of antibacterial therapy, culture should be done immediately or the sample should be placed in a preservative liquid (30% glycerol and 70% buffer solution) for no more than one day. For sowing, select lumps of mucus. The amount of Shigella in the sample can be very scarce, so inoculation is carried out on Ploskirev’s elective medium or on enrichment medium - selenite. The isolated pure culture is identified by morphology, biochemical properties and in the aglutination reaction with adsorbed species sera. Determine sensitivity to antibiotics. Shigella is one of the bacteria that quickly acquires resistance to antibiotics, in most cases associated with R-plasmids. In addition, Shigella antigens are detected in feces using ELISA. For diagnostic purposes, serological reactions are used: agg-lutination, RIGA. Antibodies appear in the second or third week of the disease. Medicinal drugs. Specific prevention has not been developed. In areas of morbidity, dysentery bacteriophage is used. Treatment with antibiotics should be carried out taking into account the sensitivity of pathogens to them. Use chloramphenicol, tetracycline; Nitrofuran preparations and polyvalent bacteriophage are effective. For chronic dysentery, vaccine therapy is used using a chemical vaccine administered orally. Klebsiella The genus Klebsiella received its name in honor of the German scientist E. Klebs. Representatives of this genus include: Klebsiella pneumoniae, Klebsiella ozaenae, Klebsiella rhinoscleromatis. Morphology, cultural properties. Klebsiella are short, thick rods. In the preparation they are located singly, in pairs and in short chains. They do not have flagella and do not form spores. A characteristic feature of Klebsiella is the formation of capsules both in the body and on nutrient media. They grow on simple nutrient media; on dense media they form mucous colonies. Their differentiation is carried out according to biochemical characteristics. Antigens. Klebsiella contains lipopolysaccharide O-antigens and polysaccharide capsular antigens, on the basis of which serotyping is carried out. Some antigens are common to those of Escherichia and Salmonella. Pathogenicity in Klebsiella is associated with the presence of a capsule that prevents phagocytosis and endotoxins. Sustainability. Klebsiella is stable in the external environment, persists for a long time in water, on objects, and in dairy products and can multiply at room temperature and in the refrigerator. They die when boiled and when exposed to disinfectants. Diseases in humans. Klebsiella pneumoniae causes inflammation of the lungs (bronchopneumonia), sometimes also sepsis, cystitis, acute intestinal infections; often found in mixed infections. Klebsiella ozena is the causative agent of chronic disease of the upper respiratory tract with the release of a viscous secretion and the formation of crusts that emit a foul odor. The disease is contagious and is transmitted by airborne droplets. Klebsiella rhinoscleroma causes a chronic inflammatory process of the mucous membranes of the upper respiratory tract, with the formation of nodules (granulomas). Immunity. Antibodies are produced during illness, but they do not provide immunity. The chronic course of the disease is associated with the development of hyperthyroidism. Laboratory diagnostics. Materials to be tested: for pneumonia - sputum, for ozena - mucus from the pharynx, nose, trachea, for rhinoscleroma - pieces of tissue from granulomas. The study is based on the isolation of pure cultures and identification by morphology, cultural, biochemical properties and determination of serovar. An RSK is performed to detect antibodies in the blood serum of patients. Medicinal drugs. Vaccine prevention has not been developed. Antibiotics (streptomycin, chloramphenicol, neomycin, tetracycline) and antimony preparations are used for treatment. Protea Among bacteria of the genus Proteus, Proteus vulgaris and Proteus mirabilis can be causative agents of food toxic infections and purulent-inflammatory processes. Morphology, cultural, biochemical properties. Proteas are polymorphic rods, short, long, filamentous, do not form spores or capsules, have flagella located peritrichially. Gram negative. They grow well on simple nutrient media. Proteas are characterized by “creeping” growth in the form of a bluish coating on dense nutrient media, which is formed by swarming H-forms. Strains that have lost flagella and the ability to swarm form colonies with smooth edges (O-form). When sowing according to the Shukevich method in condensation water at the bottom of a test tube with slanted agar, Proteus quickly covers its entire surface. Proteas have well-defined proteolytic properties: they liquefy gelatin and coagulated whey, coagulate milk, break down urea, and form hydrogen sulfide, indole, and ammonia. Many carbohydrates are fermented. Antigens. Proteas have O-antigens and H-antigens, some of which are common to other enterobacteria. Toxin formation. They do not produce exotoxin; they contain lipopolysaccharide endotoxin of the cell wall. Persistence and spread. Bacteria of the genus Proteus are widely distributed in the external environment. They are found in soil, water, and in the intestines of humans and animals. They participate in decay processes, multiplying in waste containing organic matter. Diseases in humans. Proteas are opportunistic microbes. They can cause purulent-inflammatory diseases in humans: suppuration of wounds, otitis media, peritonitis, pyelonephritis, cystitis. When eating foods containing large amounts of these bacteria, foodborne illness occurs. P. mirabilis causes purulent-inflammatory diseases of the urinary system. They can arise as a result of the introduction of bacteria with urological instruments. In newborns, the entry of Proteus into the umbilical wound leads to a septic process. Laboratory diagnostics. Depending on the disease, the materials to be tested are pus, urine, vomit, and food products. The Shukevich sowing method is used. Isolated pure cultures are identified by cultural and biochemical properties and by the agglutination reaction. Medicinal drugs. Coli-proteus bacteriophage, na-lydixic acid, and antibiotics are used. Yersinia Among bacteria belonging to the genus Yersinia, diseases in humans are caused by Yersinia peslis (the causative agent of plague), Yersinia pseudotuberculosis and Yersinia enterocolitica. Yersinia plague Yersinia pestis was discovered in 1894 by A. Yersin and S. Kitazato during the plague epidemic in Hong Kong. Morphology, cultural, biochemical properties. Y. pestis are gram-negative small ovoid-shaped rods 1-2 µm in size, immobile. They do not form spores, they have a capsule. In smears from pathological material, they are stained with methylene blue most intensely at the ends - bipolar (Fig. 31). When propagated on solid nutrient media, they look like elongated rods. Facultative anaerobes. They grow on simple nutrient media at a temperature of 28°C, but can grow at lower temperatures (up to +5°C), which can be used to isolate a pure culture. In liquid nutrient media, plague sticks form a film on the surface and threads extending down from it, similar to stalactites, and sediment in the form of flakes. On a dense nutrient medium, they form colonies that resemble a “lace handkerchief” - with a dense center and scalloped edges. Such R-forms of colonies form virulent strains, and S-forms form non-virulent strains. The characteristic cultural properties of Yersinia plague are used in identification. Carbohydrates are fermented to form acid. Proteolytic activity is weakly expressed (Table 9). Antigens. Plague sticks contain a somatic thermostable antigen, common with other Yersinia, as well as an antigen common with the erythrocytes of O-group people. Virulent strains have a capsular thermolabile antigen, which is associated with the immunogenicity of the pathogen. Pathogenicity factors. Plague bacilli form toxic substances that are contained in the body of the bacterium and in the capsule and have the properties of exo- and endotoxin. Virulence is also due to surface substances with antiphagocytic activity and enzymes: hyaluronidase, fibrinolysin, hemolysins, plasmacoagulase. Sustainability. They can survive in the external environment for a long time, tolerate low temperatures well, in frozen corpses, fleas - for a year or more, in milk - 3 months. When boiled, they die within 1 minute. Sensitive to disinfectants. Direct sunlight kills them within 2-3 hours. Diseases in humans. The main reservoir of Yersinia plague in nature is rodents (gophers, tarbagans, rats, etc.). Plague is a zoonotic disease. The source of infection for humans is animals and humans. Infection from animals occurs through transmissible means - when bitten by an infected flea, through contact. In this case, the microbe penetrates the skin. From a person suffering from pneumonic plague, the pathogen is transmitted through the air. The clinical form of plague depends on the entry point of infection. The bubonic form develops when the pathogen penetrates through the skin, followed by damage to the regional lymph nodes, which, enlarging, turn into buboes. From here, pathogens can spread through the lymphatic or blood vessels, cause damage to other lymph nodes, and lead to the development of a septic form and secondary pulmonary pneumonia. When infected through the air, primary pneumonic plague develops. In all forms of plague, the pathological process affects all organs and systems. Immunity. After an illness, immunity is stable. Laboratory diagnostics. Plague is a particularly dangerous infection. All studies are carried out in special high-security laboratories, trained personnel. The material for the study is the contents of the bubo, sputum, blood, feces, pieces of the organs of the deceased, animal corpses. If bacterioscopy of smears from the material reveals gram-negative ovoid bipolar stained rods, a preliminary diagnosis is made. Final the diagnosis is made on the basis of isolating a pure culture and its identification, morphology, cultural, biochemical, antigenic properties, sensitivity to the plague bacteriophage. These characteristics differentiate them from other types of Yersinia. They perform a biological test on guinea pigs. Also used RIF In materials from rotten animal corpses, it is possible to detect plague antigen using the precipitation reaction. Specific prevention is carried out according to epidemic indications, with a live plague vaccine containing the EV strain. Streptomycin and tetracyclines are effective among therapeutic agents. Yersinia pseudotuberculosis Yersmm pseudotuberculosis - the causative agent of pseudotuberculosis - discovered by L Malasse and R Vignal in 1883 Causes diseases characterized by the formation in organs of nodules that are externally similar to tuberculosis. One of the forms of pseudotuberculosis observed in Vladivostok is described as “Far Eastern scarlet-like fever" Morphology, cultural, biochemical properties. Gram-negative coccobacteria, do not form spores, have flagella and a capsule. Facultative anaerobes, reproduce well on simple nutrient media. An important property of pathogens for the epidemiology of the disease is their psychrophilicity. The optimal temperature for reproduction is 20-28 ° C; they also reproduce in 0 - +4°C Ferment rhamnose and urea (Table 9) Antigens. Contain O-somatic and H-flagellar antigens Serovars and subserovars are distinguished by O- and H-antigens Pathogenic factors. Yersinia pseudotuberculosis contain endotoxin, which is released when they die. Some serovars produce exotoxins Sustainability. Stable in the external environment Being psychrophiles, they can accumulate in large quantities in food products stored for a long time in the refrigerator. When boiled, they die within a few seconds, are sensitive to disinfectants Diseases in humans. The source of infection is rodents. Infection of people occurs through nutrition. Transmission factors most often are vegetable dishes (salads, vinaigrettes) and dairy products. Designations: "+" - presence of the characteristic, "-" - absence of the characteristic, "±" - sign of non-permanent products that have not been subjected to heat treatment. The water route of transmission is also important. Pathogens enter the human body through the mouth. Having overcome the protective barrier of the stomach, they enter the small intestine, resulting in gastroenteritis. The penetration of pathogens into the mesenteric nodes leads to the development of lymphadenitis with signs of irritation of the peritoneum and the formation of infiltrate (pseudotuberculous appendicitis). When Yersinia breaks through into the blood, generalized forms occur with damage to the joints, with manifestations of scarlet fever. Immunity. Antibodies are detected during the course of the disease, but they do not have a protective effect. Laboratory diagnostics Due to the wide variety of manifestations of the disease, it is crucial. The material for bacteriological research is blood, feces and vomit. Cultivation of pathogens and isolation of pure culture is carried out at their optimal temperature. Pure culture is differentiated from other Yersinias by biochemical properties. For serological diagnosis, paired sera taken at the beginning and in the third week of illness are examined in the agglutination reaction and RNGA. Medicinal drugs. Specific prevention has not been developed. For treatment, chloramphenicol and other antibiotics, nitrofuran drugs are used. The causative agent of intestinal yersiniosis Yersinia enterocolitica was described in 1939 by J. Schleifstein and M. Coleman. The spread of yersiniosis in many countries of the world has been observed since the late 60s. Morphology, cultural, biochemical properties.Y. ente-rocolitica are gram-negative polymorphic rods, they do not form spores or capsules, and have peritrichous flagella. Psychrophiles, cultivated at 20-26°C, can reproduce at lower temperatures. At 37°C they lose mobility. Grows on simple nutrient media. In terms of enzymatic properties, they are more active than other yersinia (Table 9). There are 5 biochemical variants of Y. enterocolitica. Antigens. They have O- and H-antigens. Based on O-antigens, they are divided into serovars. Toxin formation. They contain endotoxin, which is released when bacterial cells are destroyed. Some strains produce an exotoxin. The body exhibits the ability for adhesion, intracellular reproduction, and invasion (the latter is less pronounced than in Yersinia pseudotuberculosis). Sustainability. Resistant to low temperatures. At the temperature of a household refrigerator (4-8°C) they can survive for a long time and multiply on vegetables, fruits and milk. When boiled they die within a few seconds. Sensitive to disinfectants. Diseases in humans.Y. enterocolitica are widespread in nature. The source of infection is rodents and domestic animals. At the same time, pathogens can multiply in the external environment as saprophytes. Therefore, yersiniosis can be classified as a saprozoonosis. The main route of infection is nutritional. Transmission factors include contaminated meat products, vegetables, milk, and water. Having penetrated through the mouth and overcome the protective barrier of the stomach, they enter the intestine, causing inflammation of the ileum, mesenteric lymph nodes, and sometimes the appendix and cecum. Intoxication and an allergic condition develop. If pathogens enter the blood, bacteremia and generalized forms of the disease occur. Immunity. During the course of the disease, antibodies to the pathogen are detected, but immunity is not strong. Laboratory diagnostics. The materials for bacteriological examination are nasopharyngeal lavage, blood, urine, cerebrospinal fluid, and removed vermiform appendix. In optimal temperature conditions for the pathogen, a pure culture is isolated, identified by morphology and enzymatic properties, and the serovar is determined. Serological diagnosis is carried out with paired sera using the agglutination reaction, RNGA, ELISA. Medicinal drugs. Specific prevention has not been developed. For treatment, chloramphenicol and other antibiotics, biseptol, and nitrofuran drugs are used. CHOLERA VIBRIO The cholera vibrio Vibrio cholerae was first isolated from the feces of patients and corpses of those killed by cholera and studied by R. Koch in 1882 in Egypt. In 1906, F. Gottschlich, at the El Tor quarantine station in Egypt, isolated a vibrio similar to Koch's vibrio from the feces of a pilgrim. The etiological role of Vibrio eltor was recognized in 1962 by WHO. Thus, the existence of two biovars is recognized: V. cholerae and V. eltor. Morphology, cultural, biochemical properties. Vibrios cholerae have the shape of a thin curved rod, reminiscent of a comma, 2-4 microns long, gram-negative, do not form spores and capsules, have one flagellum (monotrichus), and are very mobile (Fig. 32). Very unpretentious to nutrient media. They grow well on simple alkaline nutrient media (pH 8.5-9.0), the optimal temperature for their growth is 37°C. The election medium for them is alkaline peptone water and alkaline agar. A characteristic feature of Vibrio cholerae is rapid growth. Being aerobics, they form a film on the surface of the medium in alkaline peptone water after 3-4 hours. On dense media they grow in the form of transparent bluish colonies. Vibrio cholerae exhibit enzymatic activity: they liquefy gelatin, form indole, quickly break down starch, break down maynose and sucrose to acid, do not break down arabinose (Heiberg group I), which is a test for differentiating them from other vibrios. Antigens. Vibrios have O-antigens and H-antigens. Differentiation of species is carried out by O-antigen (there are 139 of them known). Cholera vibrions - Vibrio cholerae and Vibrio eltor belong to 01. They do not differ from each other in antigenic structure. Antigen O1 consists of components A, B and C. Based on these components, cholera vibrios are divided into serovars: serovar Ogawa contains components A and B, Inaba - A and C, Gikoshima - A, B and C. In 1992 In Madras (India), and then in other Asian countries, mass cholera diseases were observed, caused by Vibrio cholerae, which has an antigen not O1, but O139. This is a new species of Vibrio cholerae O139Bengal (Bengal). There are vibrios similar to cholera, but they are not agglutinated by O-serum. They were called non-agglutinating vibrios (NAVs). NAGs are released from diarrhea and healthy people and cause gastroenteritis, which can be accompanied by intoxication. Pathogenesis factors. Vibrio cholerae produces an exo-toxin called “cholerogen”. Under the influence of cholerogens, a loss of water and sodium, potassium and chlorine ions occurs in the small intestine. They also have the ability to adhere. They are not invasive - they do not penetrate into cells or blood. Sustainability. Vibrios are sensitive to high temperature: at 60°C they die after 5 minutes, when boiled - immediately. They die quickly when dried out and exposed to light. They tolerate low temperatures well and are stored in ice for several days. They survive in food products, water, soil, and feces from several days to several weeks. Vibrios are very sensitive to acids, even low concentrations. In a solution of 1:10,000 hydrochloric and sulfuric acids, they die within a few seconds. Disinfectants in normal concentrations kill them within minutes. Vibrio eltor, compared to Vibrio cholerae, is more resistant to various external factors. Diseases in humans. Cholera is an anthroponotic infection. The source of infection is sick people and carriers. The transmission mechanism is fecal-oral, most often cholera is transmitted by water, less often by food and household contact. The incubation period for cholera ranges from several hours to 5 days. Once through the mouth into the stomach, cholera vibrios can die under the influence of acidic gastric juice. With low acidity, the risk of developing the disease is higher. Having overcome the gastric barrier, vibrios penetrate the small intestine, attach to the epithelium, and multiply. The released cholerogens cause disruption of water-salt metabolism - loss of water and salts. Clinically, this is manifested by profuse diarrhea, Immunity. During the course of the disease, antitoxins and antimicrobial antibodies are formed. Secretory IgA plays a protective role, preventing the adhesion of Vibrio cholerae on epithelial cells of the small intestine. Laboratory diagnostics. The material for research is feces and vomit, and during autopsies of corpses - a segment of the small intestine. Water, food products, as well as the intestinal contents of healthy people are also examined for carriage. Research is carried out in the laboratory of especially dangerous infections. When picking up and sending it, it is necessary to observe safety measures. Microbiological examination is important for treatment and should be carried out as soon as possible. Microscopy of a smear from the test material is preliminary. The first approximate answer can be obtained when setting up the RIF. After 5-6 hours, in crops on liquid nutrient media, the film on the surface of the medium is examined, morphology and mobility are determined, and an agglutination reaction is performed with a specific serum. The first preliminary answer is given. After 10-12 hours, the colony is studied on solid nutrient media and a second preliminary answer is given. The final answer is given after isolating and studying the pure culture. Identification of the culture is carried out on the basis of morphology, motility, agglutination with specific sera, and the study of biochemical properties. To differentiate Vibrio eltor from Vibrio cholerae, its ability to grow in a nutrient medium with polymyxin, agglutinate chicken erythrocytes, and be lysed by a specific bacteriophage is used. Preventive and therapeutic drugs. For treatment, the most important thing is to replenish the deficiency of water and electrolytes with the help of saline solutions. The use of tetracycline complements treatment and allows you to reduce the volume of administered saline solutions. For specific prevention, there are vaccines: 1) killed corpucular; 2)cholerogen-anatoxin; 3) associated vaccine (cholerogen toxoid + O-antigen).

1. First. In the Shadow of History (1877-1917) Chapter Two

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   Volume One PROLOGUE - LIFE Chapter One. IN THE HISTORICAL SHADOW (1877-1917)Chapter two. TWO TRUTHS (1917-1923)Chapter three. SCHEME AND SCHEME (1924-1925)Chapter four.

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4. Characteristics of the biological activity of exopolysaccharides from bacteria of the genus Lactobacillus and prospects for their use 03. 02. 03 microbiology

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The genus Shigella includes more than 40 serotypes. They are short, immobile gram-negative rods that do not form spores or capsules, which grow well on ordinary nutrient media and do not grow on starvation media with citrate or malonate as the only carbon source; do not form H2S, do not have urease; Voges-Proskauer reaction is negative; glucose and some other carbohydrates are fermented with the formation of acid without gas (except for some biotypes of Shigella flexneri: S. manchester and S. newcastle); As a rule, they do not ferment lactose (with the exception of Shigella Sonne), adonitol, salicin and inositol, do not liquefy gelatin, usually form catalase, and do not have lysine decarboxylase and phenylalanine deaminase. The G + C content in DNA is 49-53 mol%. Shigella are facultative anaerobes, the optimum temperature for growth is 37 ° C, they do not grow at temperatures above 45 ° C, the optimal pH of the environment is 6.7-7.2. Colonies on dense media are round, convex, translucent; in case of dissociation, rough R-form colonies are formed. Growth on MPB in the form of uniform turbidity, rough forms form a sediment. Freshly isolated cultures of Shigella Sonne usually form colonies of two types: small round convex (phase I), large flat (phase II). The nature of the colony depends on the presence (phase I) or absence (phase II) of a plasmid with a molecular weight of 120 MD, which also determines the virulence of Shigella Sonne.

The international classification of Shigella is based on their biochemical characteristics (mannitol-non-fermenting, mannitol-fermenting, slowly lactose-fermenting Shigella) and the characteristics of the antigenic structure.

Shigella have O-antigens of different specificity: common to the family Enterobacteriaceae, generic, species, group and type-specific, as well as K-antigens; They do not have N-antigens.

The classification takes into account only group and type-specific O-antigens. In accordance with these characteristics, the genus Shigella is divided into 4 subgroups, or 4 species, and includes 44 serotypes. Subgroup A (Shigella dysenteriae species) includes Shigella species that do not ferment mannitol. The species includes 12 serotypes (1-12). Each serotype has its own specific type antigen; antigenic connections between serotypes, as well as with other Shigella species, are weakly expressed. Subgroup B (Shigella flexneri species) includes Shigella, which usually ferment mannitol. Shigella of this species are serologically related to each other: they contain type-specific antigens (I-VI), according to which they are divided into serotypes (1-6/" and group antigens, which are found in different compositions in each serotype and according to which serotypes are divided into subserotypes. In addition In addition, this species includes two antigenic variants - X and Y, which do not have typical antigens; they differ in sets of group antigens. Serotype S.flexneri 6 does not have subserotypes, but it is divided into 3 biochemical types according to the characteristics of the fermentation of glucose, mannitol and dulcitol. .

Lipopolysaccharide antigen O in all Shigella Flexner contains group antigen 3, 4 as the main primary structure, its synthesis is controlled by a chromosomal gene localized near the his-locus. Type-specific antigens I, II, IV, V and group antigens 6, 7, 8 are the result of modification of antigens 3, 4 (glycosylation or acetylation) and are determined by the genes of the corresponding converting prophages, the site of integration of which is located in the lac-pro region of the Shigella chromosome.

Appeared in the country in the 80s. XX century and the widespread new subserotype S.flexneri 4 (IV:7, 8) differs from subserotype 4a (IV;3,4) and 4b (IV:3, 4, 6), arose from the variant S.flexneri Y (IV: 3, 4) due to lysogenization by its converting prophages IV and 7, 8.

Subgroup C (Shigella boydix species) includes Shigella, which usually ferment mannitol. Members of the group are serologically different from each other. Antigenic connections within the species are weakly expressed. The species includes 18 serotypes (1-18), each of which has its own main type antigen.

Subgroup D (Shigella sonnet species) includes Shigella, which usually ferment mannitol and are capable of slowly (after 24 hours of incubation and later) fermenting lactose and sucrose. The species 5. sonnei includes one serotype, but colonies of phases I and II have their own type-specific antigens. For the intraspecific classification of Shigella Sonne, two methods have been proposed:

dividing them into 14 biochemical types and subtypes according to their ability to ferment maltose, rhamnose and xylose;

division into phage types according to sensitivity to a set of corresponding phages.

These typing methods have mainly epidemiological significance. In addition, Shigella Sonne and Shigella Flexner for the same purpose are subjected to typing for the ability to synthesize specific colicins (colicino-genotyping) and for sensitivity to known colicins (colicinotyping). To determine the type of colicins produced by Shigella, J. Abbott and R. Chenon proposed sets of standard and indicator strains of Shigella, and to determine the sensitivity of Shigella to known types of colicins, the Set of reference colicinogenic strains of P. Frederick is used.

Dysentery is an infectious disease characterized by general intoxication of the body, diarrhea and a peculiar lesion of the mucous membrane of the large intestine. It is one of the most common acute intestinal diseases in the world. Dysentery has been known since ancient times under the name “bloody diarrhea,” but its nature turned out to be different. In 1875, the Russian scientist F. A. Lesh isolated the amoeba Entamoeba histolytica from a patient with bloody diarrhea; in the next 15 years, the independence of this disease was established, for which the name amoebiasis was retained.

The causative agents of dysentery itself are a large group of biologically similar bacteria, united in the genus Shigella. For the first time pathogen was discovered in 1888 by A. Chantemes and F. Vidal; in 1891 it was described by A.V. Grigoriev, and in 1898 by K. Shiga with the help received Identified serum from a patient pathogen in 34 patients with dysentery, finally proving the etiological role of this bacterium . However, in subsequent years, other pathogens were discovered dysentery : in 1900 - S. Flexner, in 1915 - K. Sonne, in 1917 - K. Stutzer and K. Schmitz, in 1932 - J. Boyd, in 1934 - D. Large, in 1943 - A. Sax.

Shigella resistance

Shigella has a fairly high resistance to environmental factors. They survive on cotton fabric and paper for up to 0-36 days, in dried feces - up to 4-5 months, in soil - up to 3-4 months, in water - from 0.5 to 3 months, on fruits and vegetables - up to 2 weeks, in milk and dairy products - up to several weeks; at a temperature of 60 C they die in 15-20 minutes. Sensitive to chloramine solutions, active chlorine and other disinfectants.

Pathogenicity factors

The most important biological property of Shigella, which determines their pathogenicity, is the ability to invade epithelial cells, multiply in them and cause their death. This effect can be detected using a keratoconjunctival test (introduction of one loop of a Shigella culture (2-3 billion bacteria) under the lower eyelid of a guinea pig causes the development of serous-purulent keratoconjunctivitis), as well as by infection of cell cultures (cytotoxic effect) or chicken embryos (their death), or intranasally in white mice (development of pneumonia). The main pathogenicity factors of Shigella can be divided into three groups:

factors determining interaction with the epithelium of the mucous membrane;

factors that ensure resistance to humoral and cellular defense mechanisms of the macroorganism and the ability of Shigella to multiply in its cells;

the ability to produce toxins and toxic products that determine the development of the pathological process itself.

The first group includes adhesion and colonization factors: their role is played by pili, outer membrane proteins and LPS. Adhesion and colonization are promoted by enzymes that destroy mucus - neuraminidase, hyaluronidase, mucinase. The second group includes invasion factors that promote the penetration of Shigella into enterocytes and their reproduction in them and in macrophages with the simultaneous manifestation of a cytotoxic and (or) enterotoxic effect. These properties are controlled by the genes of a plasmid with a molecular weight of 140 MD (it encodes the synthesis of outer membrane proteins that cause invasion) and the chromosomal genes of Shigella: ksr A (causes keratoconjunctivitis), cyt (responsible for cell destruction), as well as other genes not yet identified. Protection of Shigella from phagocytosis is provided by the surface K-antigen, antigens 3,4 and lipopolysaccharide. In addition, lipid A of Shigella endotoxin has an immunosuppressive effect: it suppresses the activity of immune memory cells.

The third group of pathogenicity factors includes endotoxin and two types of exotoxins found in Shigella - Shiga and Shiga-like exotoxins (SLT-I and SLT-II), the cytotoxic properties of which are most strongly expressed in S. dysenteriael. Shiga- and Shiga-like toxins are also found in other serotypes of S. dysenteriae; they are also produced by S.flexneri, S. sonnei, S. boydii, EHEC and some Salmonella. The synthesis of these toxins is controlled by the tox genes of converting phages. Type LT enterotoxins are found in Shigella Flexner, Sonne and Boyd. Their LT synthesis is controlled by plasmid genes. Enterotoxin stimulates the activity of adenylate cyclase and is responsible for the development of diarrhea. Shiga toxin, or non-irotoxin, does not react with the adenylate cyclase system, but has a direct cytotoxic effect. Shiga and Shiga-like toxins (SLT-I and SLT-II) have m.m. 70 kDa and consist of subunits A and B (the latter of 5 identical small subunits). The receptor for toxins is a glycolipid of the cell membrane. The virulence of Shigella Sonne also depends on a plasmid with a molecular weight of 120 MD. It controls the synthesis of about 40 outer membrane polypeptides, seven of them are associated with virulence. Shigella Sonne, having this plasmid, form phase I colonies and are virulent. Cultures that have lost the plasmid form phase II colonies and lack virulence. Plasmids see m. 120-140 MD were found in Shigella Flexner and Boyd. Shigella lipopolysaccharide is a strong endotoxin.

Post-infectious immunity

As observations of monkeys have shown, after suffering from dysentery, strong and fairly long-lasting immunity remains. It is caused by antimicrobial antibodies, antitoxins, increased activity of macrophages and T-lymphocytes. Intestinal mucosal localization mediated by IgAs plays a significant role. However, immunity is type-specific; strong cross-immunity does not occur.

Epidemiology of dysentery

The only source of infection is. No animals in nature suffer from dysentery. Under experimental conditions, dysentery can only be reproduced in monkeys. The method of infection is fecal-oral. Routes of transmission: water (predominant for Shigella Flexner), food, especially milk and dairy products (predominant route of infection for Shigella Sonne), and household contact, especially for the species S. dysenteriae.

A feature of the epidemiology of dysentery is a change in the species composition of pathogens, as well as Sonne biotypes and Flexner serotypes in certain regions. For example, until the end of the 30s. XX century S. dysenteriae 1 accounted for up to 30-40% of all cases of dysentery, and then this serotype became less and less common and almost disappeared. However, in the 1960-1980s. S. dysenteriae reappeared on the historical stage and caused a series of epidemics that led to the formation of three hyperendemic foci - in Central America, Central Africa and South Asia (India, Pakistan, Bangladesh and other countries). The reasons for the change in the species composition of dysentery pathogens are probably associated with changes in collective immunity and changes in the properties of dysentery bacteria. In particular, the return of S. dysenteriae 1 and its widespread distribution, which caused the formation of hyperendemic foci of dysentery, are associated with its acquisition of plasmids, which caused multidrug and increased virulence.

Symptoms of dysentery

The incubation period of dysentery is 2-5 days, sometimes less than a day. The formation of an infectious focus in the mucous membrane of the descending part of the large intestine (sigmoid and rectum), where the dysentery pathogen penetrates, is cyclical in nature: adhesion, colonization, introduction of Shigella into the cytoplasm of enterocytes, their intracellular reproduction, destruction and rejection of epithelial cells, release of pathogens into the lumen intestines; after this, the next cycle begins - adhesion, colonization, etc. The intensity of the cycles depends on the concentration of pathogens in the parietal layer of the mucous membrane. As a result of repeated cycles, the inflammatory focus grows, the resulting ulcers, connecting, increase the exposure of the intestinal wall, as a result of which blood, mucopurulent lumps, and polymorphonuclear leukocytes appear in the feces. Cytotoxins (SLT-I and SLT-II) cause cell destruction, enterotoxin – diarrhea, endotoxins – general intoxication. The clinical picture of dysentery is largely determined by what type of exotoxin is produced to a greater extent by the pathogen, the degree of its allergenic effect and the immune status of the body. However, many questions of the pathogenesis of dysentery remain unclear, in particular: the features of the course of dysentery in children of the first two years of life, the reasons for the transition of acute dysentery to chronic, the significance of sensitization, the mechanism of local immunity of the intestinal mucosa, etc. The most typical clinical manifestations of dysentery are diarrhea, frequent urge: in severe cases, up to 50 or more times a day, tenesmus (painful spasms of the rectum) and general intoxication. The nature of the stool is determined by the degree of damage to the large intestine. The most severe dysentery is caused by S. dysenteriae 1, the mildest is Sonne's dysentery.

Laboratory diagnosis of dysentery

The main method is bacteriological. The material for research is feces. Pathogen isolation scheme: inoculation on differential diagnostic media Endo and Ploskirev (in parallel on enrichment medium followed by inoculation on Endo and Ploskirev media) to isolate isolated colonies, obtaining a pure culture, studying its biochemical properties and, taking into account the latter, identification using polyvalent and monovalent diagnostic agglutinating sera. The following commercial serums are produced.

For Shigella that do not ferment mannitol:

to S. dysenteriae 1 and 2 (polyvalent and monovalent),

to S. dysenteriae 3-7 (polyvalent and monovalent),

to S. dysenteriae 8-12 (polyvalent and monovalent).

To Shigella fermenting mannitol: to typical antigens S. flexneri I, II, III, IV, V, VI, to group antigens S.flexneri 3, 4, 6,7,8 - polyvalent, to antigens S. boydii 1-18 (polyvalent and monovalent), to S. sonnei antigens phase I, phase II, to S. flexneri antigens I-VI + S. sonnei - polyvalent.

To quickly identify Shigella, the following method is recommended: a suspicious colony (lactose-negative on Endo medium) is subcultured on TSI (triple sugar iron) medium - triple sugar agar (glucose, lactose, sucrose) with iron to determine H2S production; or to a medium containing glucose, lactose, sucrose, iron and urea.

Any organism that breaks down urea after 4 to 6 hours of incubation is most likely a member of the genus Proteus and can be excluded. An organism that produces H,S, or has a urease, or produces an acid on the joint (ferments lactose or sucrose) can be excluded, although H2S-producing strains should be investigated as possible members of the genus Salmonella. In all other cases, the culture grown on these media should be examined and, if it ferments glucose (change in the color of the column), isolated in its pure form. At the same time, it can be tested in a glass agglutination reaction with appropriate antisera to the genus Shigella. If necessary, other biochemical tests are carried out to check whether they belong to the genus Shigella, and also study motility.

To detect antigens in the blood (including as part of the CEC), urine and feces, the following methods can be used: RPGA, RSK, coagglutination reaction (in urine and feces), IFM, RAGA (in blood serum). These methods are highly effective, specific and suitable for early diagnosis.

For serological diagnosis, the following can be used: RPHA with the corresponding erythrocyte diagnostics, immunofluorescence method (indirect modification), Coombs method (determining the titer of incomplete antibodies). An allergy test with dysenterine (a solution of protein fractions of Shigella Flexner and Sonne) is also of diagnostic value. The reaction is taken into account after 24 hours. It is considered positive in the presence of hyperemia and infiltrate with a diameter of 10-20 mm.

Treatment of dysentery

The main attention is paid to restoring normal water-salt metabolism, rational nutrition, detoxification, rational antibiotic therapy (taking into account the sensitivity of the pathogen to antibiotics). A good effect is achieved by early use of a polyvalent dysentery bacteriophage, especially tablets with pectin coating, which protects the phage from the action of HC1 gastric juice; In the small intestine, pectin dissolves, phages are released and exert their effect. For preventive purposes, the phage should be given at least once every three days (the period of its survival in the intestine).

Specific prevention of dysentery

To create artificial immunity against dysentery, various vaccines were used: from killed bacteria, chemical, alcohol, but all of them turned out to be ineffective and were discontinued. Vaccines against Flexner's dysentery have been created from live (mutant, streptomycin-dependent) Shigella Flexner; ribosomal vaccines, but they also have not found widespread use. Therefore, the problem of specific dysentery remains unresolved. The main way to combat dysentery is to improve the water supply and sewerage system, ensure strict sanitary and hygienic regimes in food enterprises, especially the dairy industry, in child care institutions, public places and in maintaining personal hygiene.

Preliminary conclusion: according to biochemical characteristics, the isolated culture corresponds to Shigella subgroup _______________________________

4. Carry out an agglutination reaction on glass of the isolated culture with type-specific sera to Flexner's Shigella (1,2,3), compare the results obtained with Table 3, and give a conclusion.

Table 3

Classification of Shigella by antigenic structure

Conclusion: Shigella flexneri was isolated from the patient's stool;

serovar ______________________________________________________________

5. Supplement the scheme for laboratory diagnosis of dysentery.

Researchable

material:

	Stage I Stage II
Stage III						RA with species, type, subtype diagnostic sera

List the properties of Shigella necessary to determine their species, type and subtype: _____________________________________________________________________

____________________________________________________________________________________

6. List the pathogenicity factors of Shigella: __________________________
________________________________________________________________________________________________________________________________________________

III. Study diagnostic preparations (diagnostic immune sera, diagnosticums, antigens)

Teacher's signature ______________________________

Date of__________________

Lesson 4

Subject: Salmonella typhoid, paratyphoid and gastroenteritis. Laboratory diagnostics of salmonellosis.

Issues for discussion:

1. Classification of Salmonella. Key features in identifying salmonella.

2. Factors of pathogenicity of typhoid Salmonella and the pathogenesis of the disease.

3. Stages of laboratory diagnosis of typhoid fever in the dynamics of the disease.

4. Pathogenicity factors of Salmonella – causative agents of gastroenteritis.

5. Laboratory diagnosis of Salmonella gastroenteritis.

6. Prevention of typhoid fever, paratyphoid fever and salmonella gastroenteritis.

Practical tasks:

I. Bacteriological examination of the patient’s blood.

1. Study the result of culturing blood cultures in 10% bile broth and note changes in the medium.

3. Determine the enzymatic properties of the isolated blood culture in Olkenitsky’s medium and give a preliminary conclusion.

4. Study the biochemical properties of Salmonella in Hiss media (demonstration) and compare them with the data presented in Table 1.

Shigella has a fairly high resistance to environmental factors. They survive on cotton fabric and paper for up to 0-36 days, in dried feces - up to 4-5 months, in soil - up to 3-4 months, in water - from 0.5 to 3 months, on fruits and vegetables - up to 2 weeks, in milk and dairy products - up to several weeks; at a temperature of 60 C they die in 15-20 minutes. Sensitive to chloramine solutions, active chlorine and other disinfectants.

Pathogenicity factors of Shigella

The most important biological property of Shigella, which determines their pathogenicity, is the ability to invade epithelial cells, multiply in them and cause their death. This effect can be detected using a keratoconjunctival test (introduction of one loop of a Shigella culture (2-3 billion bacteria) under the lower eyelid of a guinea pig causes the development of serous-purulent keratoconjunctivitis), as well as by infection of cell cultures (cytotoxic effect) or chicken embryos (their death), or intranasally in white mice (development of pneumonia). The main pathogenicity factors of Shigella can be divided into three groups:

• factors determining interaction with the epithelium of the mucous membrane;
• factors that ensure resistance to humoral and cellular defense mechanisms of the macroorganism and the ability of Shigella to multiply in its cells;
• the ability to produce toxins and toxic products that determine the development of the pathological process itself.

The first group includes adhesion and colonization factors: their role is played by pili, outer membrane proteins and LPS. Adhesion and colonization are promoted by enzymes that destroy mucus - neuraminidase, hyaluronidase, mucinase. The second group includes invasion factors that promote the penetration of Shigella into enterocytes and their reproduction in them and in macrophages with the simultaneous manifestation of a cytotoxic and (or) enterotoxic effect. These properties are controlled by the genes of a plasmid with a molecular weight of 140 MD (it encodes the synthesis of outer membrane proteins that cause invasion) and the chromosomal genes of Shigella: ksr A (causes keratoconjunctivitis), cyt (responsible for cell destruction), as well as other genes not yet identified. Protection of Shigella from phagocytosis is provided by the surface K-antigen, antigens 3,4 and lipopolysaccharide. In addition, lipid A of Shigella endotoxin has an immunosuppressive effect: it suppresses the activity of immune memory cells.

The third group of pathogenicity factors includes endotoxin and two types of exotoxins found in Shigella - Shiga and Shiga-like exotoxins (SLT-I and SLT-II), the cytotoxic properties of which are most strongly expressed in S. dysenteriael. Shiga- and Shiga-like toxins are also found in other serotypes of S. dysenteriae; they are also produced by S.flexneri, S. sonnei, S. boydii, EHEC and some Salmonella. The synthesis of these toxins is controlled by the tox genes of converting phages. Type LT enterotoxins are found in Shigella Flexner, Sonne and Boyd. Their LT synthesis is controlled by plasmid genes. Enterotoxin stimulates the activity of adenylate cyclase and is responsible for the development of diarrhea. Shiga toxin, or non-irotoxin, does not react with the adenylate cyclase system, but has a direct cytotoxic effect. Shiga and Shiga-like toxins (SLT-I and SLT-II) have m.m. 70 kDa and consist of subunits A and B (the latter of 5 identical small subunits). The receptor for toxins is a glycolipid of the cell membrane. The virulence of Shigella Sonne also depends on a plasmid with a molecular weight of 120 MD. It controls the synthesis of about 40 outer membrane polypeptides, seven of them are associated with virulence. Shigella Sonne, having this plasmid, form phase I colonies and are virulent. Cultures that have lost the plasmid form phase II colonies and lack virulence. Plasmids see m. 120-140 MD were found in Shigella Flexner and Boyd. Shigella lipopolysaccharide is a strong endotoxin.

Post-infectious immunity

As observations of monkeys have shown, after suffering from dysentery, strong and fairly long-lasting immunity remains. It is caused by antimicrobial antibodies, antitoxins, increased activity of macrophages and T-lymphocytes. Local immunity of the intestinal mucosa, mediated by IgAs, plays a significant role. However, immunity is type-specific; strong cross-immunity does not occur.

Epidemiology of dysentery

The source of infection is only humans. No animals in nature suffer from dysentery. Under experimental conditions, dysentery can only be reproduced in monkeys. The method of infection is fecal-oral. The modes of transmission are water (predominant for Shigella Flexner), food, a particularly important role is played by milk and dairy products (predominant route of infection for Shigella Sonne), and household contact, especially for the species S. dysenteriae.

A feature of the epidemiology of dysentery is a change in the species composition of pathogens, as well as Sonne biotypes and Flexner serotypes in certain regions. For example, until the end of the 30s. XX century S. dysenteriae 1 accounted for up to 30-40% of all cases of dysentery, and then this serotype became less and less common and almost disappeared. However, in the 1960-1980s. S. dysenteriae reappeared on the historical stage and caused a series of epidemics that led to the formation of three hyperendemic foci - in Central America, Central Africa and South Asia (India, Pakistan, Bangladesh and other countries). The reasons for the change in the species composition of dysentery pathogens are probably associated with changes in collective immunity and changes in the properties of dysentery bacteria. In particular, the return of S. dysenteriae 1 and its widespread distribution, which caused the formation of hyperendemic foci of dysentery, are associated with its acquisition of plasmids that caused multidrug resistance and increased virulence.

Symptoms of dysentery

The incubation period of dysentery is 2-5 days, sometimes less than a day. The formation of an infectious focus in the mucous membrane of the descending part of the large intestine (sigmoid and rectum), where the dysentery pathogen penetrates, is cyclical in nature: adhesion, colonization, introduction of Shigella into the cytoplasm of enterocytes, their intracellular reproduction, destruction and rejection of epithelial cells, release of pathogens into the lumen intestines; after this, the next cycle begins - adhesion, colonization, etc. The intensity of the cycles depends on the concentration of pathogens in the parietal layer of the mucous membrane. As a result of repeated cycles, the inflammatory focus grows, the resulting ulcers, connecting, increase the exposure of the intestinal wall, as a result of which blood, mucopurulent lumps, and polymorphonuclear leukocytes appear in the feces. Cytotoxins (SLT-I and SLT-II) cause cell destruction, enterotoxin - diarrhea, endotoxins - general intoxication. The clinical picture of dysentery is largely determined by what type of exotoxin is produced to a greater extent by the pathogen, the degree of its allergenic effect and the immune status of the body. However, many questions of the pathogenesis of dysentery remain unclear, in particular: the features of the course of dysentery in children of the first two years of life, the reasons for the transition of acute dysentery to chronic, the significance of sensitization, the mechanism of local immunity of the intestinal mucosa, etc. The most typical clinical manifestations of dysentery are diarrhea, frequent urge: in severe cases, up to 50 or more times a day, tenesmus (painful spasms of the rectum) and general intoxication. The nature of the stool is determined by the degree of damage to the large intestine. The most severe dysentery is caused by S. dysenteriae 1, the mildest is Sonne's dysentery.

To Shigella fermenting mannitol: to typical antigens S. flexneri I, II, III, IV, V, VI, to group antigens S.flexneri 3, 4, 6,7,8 - polyvalent, to antigens S. boydii 1-18 (polyvalent and monovalent), to S. sonnei antigens phase I, phase II, to S. flexneri antigens I-VI + S. sonnei - polyvalent.

To quickly identify Shigella, the following method is recommended: a suspicious colony (lactose-negative on Endo medium) is subcultured on TSI (triple sugar iron) medium - triple sugar agar (glucose, lactose, sucrose) with iron to determine H2S production; or to a medium containing glucose, lactose, sucrose, iron and urea.

Any organism that breaks down urea after 4 to 6 hours of incubation is most likely a member of the genus Proteus and can be excluded. An organism that produces H,S, or has a urease, or produces an acid on the joint (ferments lactose or sucrose) can be excluded, although H2S-producing strains should be investigated as possible members of the genus Salmonella. In all other cases, the culture grown on these media should be examined and, if it ferments glucose (change in the color of the column), isolated in its pure form. At the same time, it can be tested in a glass agglutination reaction with appropriate antisera to the genus Shigella. If necessary, other biochemical tests are carried out to check whether they belong to the genus Shigella, and also study motility.

To detect antigens in the blood (including as part of the CEC), urine and feces, the following methods can be used: RPGA, RSK, coagglutination reaction (in urine and feces), IFM, RAGA (in blood serum). These methods are highly effective, specific and suitable for early diagnosis.

For serological diagnosis, the following can be used: RPHA with the corresponding erythrocyte diagnostics, immunofluorescence method (indirect modification), Coombs method (determining the titer of incomplete antibodies). An allergy test with dysenterine (a solution of protein fractions of Shigella Flexner and Sonne) is also of diagnostic value. The reaction is taken into account after 24 hours. It is considered positive in the presence of hyperemia and infiltrate with a diameter of 10-20 mm.

Specific prevention of dysentery

To create artificial immunity against dysentery, various vaccines were used: from killed bacteria, chemical, alcohol, but all of them turned out to be ineffective and were discontinued. Vaccines against Flexner's dysentery have been created from live (mutant, streptomycin-dependent) Shigella Flexner; ribosomal vaccines, but they also have not found widespread use. Therefore, the problem of specific prevention of dysentery remains unresolved. The main way to combat dysentery is to improve the water supply and sewerage system, ensure strict sanitary and hygienic regimes in food enterprises, especially the dairy industry, in child care institutions, public places and in maintaining personal hygiene.

Genus Shigella .

Shigella is an intestinal pathogen of humans and primates that causes bacillary dysentery or shigellosis. In accordance with the antigenic structure of the O-antigen and biochemical properties, the known serotypes of Shigella are divided into four species or serogroups - S.dysenteriae (serogroup A), S.flexneri (serogroup B), S.boydii (serogroup C) and S.sonnei (serogroup D).

By morphological characteristics Shigella is no different from other enterobacteria. These are non-specific facultative anaerobic gram-negative rods.

Biochemical properties . Shigella is biochemically inactive compared to other intestinal bacteria. They do not form hydrogen sulfide on three-sugar iron agar and do not ferment urea.

Strains of S.dysenteriae (serogroup A) have the least enzymatic activity, fermenting only glucose without gas formation; unlike other Shigella, this species is mannitol-negative.

Shigella Flexner ferments mannitol and produces indole, but does not ferment lactose, dulcite and xylose. The Newcastle serotype is divided into three biochemical types. For Shigella Flexner, the waterborne route of transmission is more typical.

Boyd's Shigella (serogroup C) have similar biochemical activity, but ferment dulcite, xylose and arabinose. They have a number of serotypes, each of which has its own main type antigen.

Shigella Sonne (serogroup D) is capable of slowly fermenting lactose and sucrose and has biochemical types and phagotypes. The main route of transmission is food (usually through milk and dairy products).

Antigenic structure . Shigella has O- and K-antigens. O-antigens have epitopes of varying specificity - from those common to the family of enterobacteria to type-specific ones. The classification takes into account only thermostable group (four groups or types - A, B, C and D) and type-specific (division into serotypes). Heat-labile antigens include K-antigens (they are found in groups A and C) and fimbrial antigens (in Shigella Flexner they are antigenically similar to E.coli). Determination of the antigenic structure is necessary for final identification.

Epidemiology . Shigella is quite stable in the external environment. The source of infection is a person with various forms of clinical manifestations of shigellosis. The mechanism of infection is fecal-oral. Different types of Shigella are characterized by the predominant routes of transmission (contact-household - for S.dysenteriae, food - for S.sonnei, water - for S.flexneri). The epidemic process is characterized by a change in the structure of circulating populations of pathogens - a change in leading species, biovars, serovars, which is associated both with changes in population immunity and with changes in the properties of the pathogen, especially with the acquisition of various plasmids (R, F, Col, etc.). The infectious dose is about 200 - 300 Shigella. Dysentery caused by Shigella Sonne has a milder course.

Pathogenicity factors and pathogenesis of lesions . The main biological characteristic of Shigella is the ability to invade epithelial cells, multiply in them and cause their death. The formation of a lesion in the mucosa of the descending colon (sigmoid and rectum) is cyclical: adhesion, colonization, introduction of Shigella into the cytoplasm of enterocytes, reproduction, destruction and rejection of epithelial cells, release of Shigella into the intestinal lumen, adhesion again, etc.

Role adhesion and colonization factors performed by pili, outer membrane proteins, LPS, enzymes - neuraminidase, mucinase, hyaluronidase (destroy mucus).

Shigella has a range of factors of invasion and resistance to the action of defense mechanisms (K-antigen, LPS, etc.) controlled by Shigella chromosomal genes and plasmids.

Shigella have different toxins. They have endotoxin and Shiga-like cytotoxins (SLT-1, SLT-2). Cytotoxins cause cell destruction, enterotoxin causes diarrhea, and endotoxin causes general intoxication. Shiga Toxin causes disruption of protein synthesis, absorption of sodium and water ions, and fluid influx into the site of inflammation.

The most typical signs of dysentery are diarrhea, tenesmus(painful spasms of the rectum) and frequent urges, general intoxication. The nature of the stool is determined by the degree of damage to the large intestine.

Post-infectious immunity - durable, type-specific.

Laboratory diagnostics . The main diagnostic method is bacteriological. The feces are inoculated on the differential diagnostic media Endo and Ploskirev to obtain isolated colonies. Pure cultures are studied according to their biochemical properties, identification is carried out in RA with poly- and monovalent sera. If the isolated culture has the biochemical properties of Shigella, but does not agglutinate sera to O-antigens, it must be boiled for 30 minutes to destroy heat-labile K-antigens, which often prevent agglutination of Shigella serogroups A and C (i.e., having K-antigens), and again research in RA.

For serological diagnosis, RPGA with group erythrocyte diagnostics is used.

Characteristics of the genus Shigella ( Shigella )

Causes Shigelosis (formerly dysentery)

It is characterized by specific damage to the large intestine, intoxication, and diarrhea.

The name comes from the Japanese Shiga. In 1898 he described it, before him Vidal and Chentemes.

Morphology – rods 0.4-0.8 microns thick, 1-2 microns long. They do not have spores or capsules, and Shigella does not have flagella. They are not mobile.

Classification.

The genus Shigella includes 4 species.

1st species – Shigella dysenteriae (S.dysenteriae) 1-12 serovars, does not break down monitis.

2nd type – Shigella flexera (S.Dlecneri1-7,x,y)

3rd species – Shigella Boyda (S.Boydu1-18)

4th species - S.zonnei - has no serotypes, breaks down mannitol, sucrose, lactose.

Cultural properties– grow well on simple nutrient media, facultative anaerobes. Optimumph – 7.S – growth form. On differential media with lactose there are transparent, colorless colonies.

Enzymatic properties are lower than others. Breaks down sugars only to acid, does not form hydrogen sulfide. In relation to lactose, S.Zonnein breaks down within 2-3 days.

Antigens- have an O antigen, which determines type specificity, and a K antigen. No antigen, because there are no flagella and they are not motile.

Resistance to environmental factors. In feces, soil - 3-5 months, in running water - 3 months, on vegetables and fruits 2 weeks. When boiled, they die instantly. Highly sensitive to disinfectant. Means.

Pathogenicity – very high adhesive properties. There are membrane proteins that ensure the attachment of Shigella to the epithelium of the distal parts of the large intestine. Highly invasive. Like all Gr(-) they contain endotoxin, which has the properties of a cytotoxin - this toxin is called Shego toxin. If found in other bacteria, it is called Shego-like.

There are antiphagocytic properties, pathogenicity factors are determined not only in chromosomal, but also in plasmid genes.

Pathogenesis and blade. The incubation period is 1-7 days. A focus is formed in the mucosa where microbes attach, colonize, invade the cytoplasm, cause cell death, and enter subsequent cells. In such patients, mucus and blood appear in the stool; clinicians say that the stool is like raspberry jelly.

Immunity is type-specific, titers are low, low tension, so repeated cases may occur.

Laboratory diagnostics– rectal mucus, sanitary objects, surface washes, water samples.

Primary seeding is carried out simultaneously on both accumulative media and media with lactose. A special environment is Ploskireva. After obtaining lactose negative colonies. They are subcultured on Ressel's medium for culture accumulation and then final identification is carried out based on biochemical and antigenic properties. All other methods are uninformative and are not used.

Specific prevention is an alcohol-killed vaccine, but it is not very effective and is practically not used even for epidemiological indications.