Shigella morphology. Medical microbiology, immunology and virology
Dysentery is an acute infectious disease that occurs with primary damage to the mucous membrane of the distal part of the large intestine and general intoxication.
The causative agent is a group of microorganisms of the genus Shigella of the Enterobacteriaceae family.
In 1891, A.V. Grigoriev discovered the causative agent of dysentery in human corpses and described it. In 1898, Japanese researcher Shiga isolated a pure culture of dysentery bacteria and proved their role in the occurrence of the disease. Later, other types of bacteria that cause dysentery were isolated and described (Flexner, Sonne, Stutzer-Schmitz).
According to the International Classification, the genus Shigella is divided into four groups: A. Sh..-dysenteriae, B. Sh.-flexneri, C. Sh.-Boudii, O. Sh.-Sonnei. The first included bacteria Grigoriev - Shig, Shtutser - Schmitz, Large - Sachs, the second - the Newcastle subspecies. In addition, each group, with the exception of Sh.-Sonnei, has a different number of serological variants (sero-types).
Morphology and tinctorial properties Shigella are the same as other representatives of the Enterobacteriaceae family. The exception is the absence of flagella, so pathogens
Theria are immobile. On the surface of the cell there are short villi (pili).
Cultural properties. Shigella is undemanding to nutrient media. They reproduce on MPA and MPB at a temperature of 37 0 WITH and pH 7.2-7.4. On dense media, colonies are small (1.5-2 mm in diameter), round, translucent, S-shaped. . Sh.-Sonnei 1 also form R-form colonies - large, flat, with jagged edges.
The growth of Shigella on MPB is accompanied by a diffuse turbidity of the medium. Differential diagnostic for dysentery microbes are Endo, Levin, EMS media, on which Shigella grows in the form of colorless, transparent colonies.
Enzymatic properties. Shigella ferments carbohydrates
with the formation of acid without gas; they break down glucose and do not ferment lactose (except for Shigella Sonne). In relation to mannitol, all dysentery bacteria are divided into mannitol-positive (. Sh.-flexneri, . Sh.-Boudii, . Sh.-Sonnei) and mannitol-negative (Sh..-dysenteriae). The ability to break down proteins is weakly expressed: indole and hydrogen sulfide are formed inconsistently, milk is not curdled, gelatin is not liquefied; reduce nitrates to nitrites.
Antigenic structure. Shigella contains somatic antigen and surface K-antigen.
Pathogenicity factors. The virulent properties of Shigella are determined by their adhesion to the mucous membrane of the large intestine, penetration into the intestinal epithelial cells and reproduction in them, the formation of exo- and endotoxins.
Exotoxin is produced by Grigoriev-Shiga bacteria. It is a protein, thermolabile, has a neurotoxic and enterotoxic effect on the human body, monkeys, dogs, and rabbits. The remaining species of Shigella form a heat-stable endotoxin, which is a lipoid-polysaccharide-protein complex.
Resistance. The causative agents of bacterial dysentery persist for five to ten days in water, soil, and on various products and objects. At low temperatures, Shigella remains viable for up to two months, at a temperature of 100 0 ° C they die instantly, and at 60 ° C - after 20-30 minutes;
direct sunlight, generally accepted concentrations of disinfectant solutions cause the death of dysentery bacilli in 20-30 minutes. The bacteria of Grigoriev - Shiga are the least stable in the external environment, and the most - Sonne and Boyd.
Epidemiology. The source of infection is humans. Patients with mild and erased forms of acute dysentery, those suffering from chronic dysentery and healthy bacteria carriers pose a great epidemiological danger. Fur-
The mode of transmission of infection is fecal-oral. The implementation of this mechanism is carried out through food (vegetables, fruits, salads, milk), water, through dirty hands and contaminated objects (toys, etc.). Flies play a certain role in the transmission of infection.
Dysentery occurs in sporadic cases and epidemic outbreaks. It has a pronounced seasonality (the maximum of the disease occurs in July - September). All age groups of the population are affected, but children are more often affected.
Pathogenesis. The development of the disease depends on the type of Shigella, the dose of the pathogen, and the condition of the body. Shigella, having entered the stomach through the mouth, can remain in it for a day or more, while some of them are destroyed, releasing endotoxin. The remaining bacteria move into the small intestine, where they can linger for up to several days and even multiply, which disrupts its motor, absorption and digestive functions. Shigella then enters the lower parts of the gastrointestinal tract, localizing in the distal part of the large intestine.
An important role in the pathogenesis of dysentery belongs to toxins that are absorbed from the intestine into the blood and affect the intestinal mucosa and the vessels located in it, nerve endings, etc.; to the central nervous system, and also cause specific sensitization.
Damage to the mucous membrane, mainly of the distal colon (swelling, hemorrhages, erosions, ulcers), is a consequence of trophic disorders that develop as a result of the damaging effect of dysentery toxin on the peripheral nerve ganglia. The allergic factor plays a certain role in the pathogenesis of dysentery.
Clinic. The incubation period lasts from one to seven days (usually two or three). In typical cases, the disease begins acutely. In the clinical manifestations of dysentery, two main syndromes are distinguished: general intoxication syndrome and colon lesion syndrome. General intoxication is characterized by increased body temperature, chills, a feeling of heat, decreased appetite, adynamia, headache, and weakness.
Signs of damage to the gastrointestinal tract are various types of pain. At first they are usually dull, spread over the entire abdomen, and of a constant nature; then they become more acute, cramping, localized in the lower abdomen, often on the left, and intensify before defecation. There are also peculiar pain sensations - tenesmus (pulling pain in the rectal area during defecation and for 5-15 minutes after it), false urge to lower, a prolonged act of defecation, a feeling of its incompleteness. Stools are frequent (from two to five to 10 or more times a day), bowel movements are initially fecal in nature.
character, then streaks of mucus and blood appear in them. In more severe cases, only a small amount of bloody mucus is released during bowel movements.
By clinical manifestations dysentery is divided into acute, chronic and post-dysenteric intestinal dysfunctions.
Immunity. The transferred disease leaves behind a short-term, species- and type-specific immunity. For diseases caused by Grigoriev-Shiga bacteria, it is more persistent and antitoxic.
Laboratory diagnostics based on bacteriological and serological studies. For bacteriological analysis, patients take stool (mandatory before prescribing etiotropic drugs) or lumps of mucus, pus, blood in stool and inoculate on Petri dishes with differential diagnostic media Endo, EMS, Ploskirev and on selenite medium containing phenol derivatives, which inhibit the growth of concomitant microflora. After 18-24 hours of incubation in a thermostat, colorless lactose-negative colonies are selected on plates and subcultured onto slanted agar to isolate a pure culture, which is identified by biochemical properties and antigenic structure.
For serological For the diagnosis of dysentery, the indirect hemagglutination reaction (IRHA) with erythrocyte diagnostics is used. RNGA is carried out repeatedly with an interval of at least seven days (“paired sera”). Diagnostic value has a fourfold increase in antibody titer, which is detected from the 10-12th day of illness.
Treatment must be timely and comprehensive. In severe forms of dysentery, ampicillin and doxycycline are prescribed as etiotropic drugs; for moderate cases - antibiotics of the tetracycline group, chloramphenicol, bactrim is also effective; for mild forms, nitrofuran drugs (furazolidone, furadonin, furazolin) are used. 8-hydroxyquinoline derivatives (enteroseptol), sulfonamides (phtazin, sulgin, phthalazole, sulfadimethoxine) are also used. In addition to etiotropic therapy, if necessary, pathogenetic treatment is carried out (saline solutions, glucose solution, prednisolone are administered intravenously). For chronic dysentery and to prevent the formation of bacterial carriage, vaccine therapy is indicated (the Chernokhvostov vaccine is used). A mandatory component of treatment for all forms of dysentery is nutritional therapy.
Prevention dysentery should include a set of measures aimed at identifying the source of infection and suppressing its transmission routes. Rapid recognition of the disease and correct and timely treatment are important. One
One of the methods of prevention is compliance with sanitary and hygienic standards: sanitary supervision of water supply and sewerage, control at catering establishments and the food industry, especially dairy. Compliance with the rules of personal hygiene and the fight against flies plays an important role. There are no specific prevention methods.
Proteus
Microorganisms of the genus Proteus, isolated in 1885 by G. Hauser, taxonomically belong to the family Enterobacteriaсeae and include five species: Pr. vulgaris, Pr. mirabilis, Pr. morganii, Pr. rettgeri, Pr. inconstans.
Most species of proteas live in open water, sewage and soil. Pr. vulgaris is often found as part of the normal intestinal microflora; Pr. morganii is isolated from summer diarrhea in children, and Pr. rettgeri and Pr. inconstans. characterized as causative agents of hospital infections.
Morphology. Proteus is a gram-negative polymorphic rod 1-3 microns long and 0.4-0.6 microns wide. In the smear, bacterial individuals are arranged in pairs or in chains, do not form spores or capsules, and are mobile (peritrichous).
According to the type of respiration, Proteas are facultative anaerobes; they grow well on simple nutrient media at an optimum temperature of 25-37 ° C. On MPB, growth is manifested by diffuse turbidity of the medium; on MPA, colonies are formed in the H- or 0-form. In the H-form (typical), colonies are formed in the form of “swarming” zones due to the “spreading” of daughter generations of microbial cells. When sowing agar slants into condensation water using the Shukevich method, the surface of the nutrient medium becomes covered with a bluish-silver coating.
If there are substances in the nutrient medium that inhibit motility (phenol, brilliant green, bile, acridine compounds, phenylethyl alcohol or 0.1% chloral hydrate), large colonies with smooth edges are formed.
Proteus rods have a wide range of enzymatic properties, the severity of which allows for species differentiation based on their selective ability to ferment maltose (Pr. vulgaris), mannitol and innositol (Pr. rettgeri), liquefy gelatin and form hydrogen sulfide (Pr. vulgaris, Pr. mirabilis ), exhibit ornithine decarboxylase activity (Pr. morganii, Pr. rettgeri).
Antigenic structure. Proteus rods contain a thermostable somatic 0-antigen and a thermolabile flagellar H-anti-
gene. According to Kaufman's classification, Pr. vulgaris, Pr. mirabilis, Pr. morganii have 66, Pr. rettgeri - 45 and Pr. inconstans - 156 sero vars. Some strains (Proteus OX) exhibit antigenic similarity to lipopolysaccharide complexes of rickettsiae, as a result of which they were used in the Weigl-Felix agglutination reaction to diagnose rickettsial diseases.
Pathogenicity factors. Bacteria of the genus Proteus are opportunistic microorganisms and are capable of exhibiting pathogenicity in a weakened body or when they enter tissues with impaired defense mechanisms. The main pathogenicity factor is endotoxin.
Epidemiology. The main source of infection is a person who excretes Proteus bacilli in their feces; The main routes of transmission are fecal-oral and contact-household.
Pathogenesis and clinic. The pathogenesis of Proteus infections is based on the ability of the pathogen to cause the development of foci of purulent inflammation in the body. Proteus food toxic infections, otitis, conjunctivitis, pyelonephritis, cystitis, and in severe cases of septicopyemia with endotoxic shock, which often ends in death, are noted.
Immunity. After a proteus infection, a mild, short-term antimicrobial immunity is formed.
Laboratory diagnostics. Same type for intestinal infections.
Treatment and prevention. For treatment, polymyxin, gentamicin, kanamycin, carbenicillin, furazolidone, chloramphenicol, etc. are used. There are no specific methods of prevention. To prevent the spread of Proteus infection, microbial contamination of water and food products should be prevented and sanitary and hygienic standards should be observed.
Klebsiella (K1ebsie11a)
The genus K1ebsie11a is part of the family Enterobacteriaceae and consists of the species: K. pneumoniae (causative agent of catarrhal pneumonia), K. rhinoscleromatis (causative agent of rhinoscleroma) and K. ozaenae (causative agent of ozena).
The unifying morphological feature for all types of Klebsiella is the ability to form a mucous capsule, which is most clearly expressed in strains freshly isolated from the body and is lost during long-term cultivation.
Klebsiella persists in sick and healthy people on the mucous membrane of the nose, pharynx and respiratory tract. They are also found in soil, water and on plants.
Morphology. Klebsiella look like thick short rods with rounded ends, their length is 0.6-6, and their width is 0.3-1.5 microns. In the smear they are located singly, in pairs or in the form of short chains; usually surrounded by a capsule. Motile, do not form spores. K. pneumoniae and K. ozaenae have pili. Gram staining is negative.
Cultural properties. Klebsiella are facultative anaerobes, growing on simple nutrient media with a pH of 7.2 at a temperature of 35-37 °C. Growth on liquid nutrient media is manifested by intense turbidity; on agar, mucous, cloudy colonies of different structures are formed in the form of S- and R-forms.
Enzymatic properties. Klebsiella does not have proteolytic properties, does not produce indole and hydrogen sulfide. Saccharolytic properties are also weakly expressed. The assessment of the enzymatic activity of Klebsiella species in relation to glucose, dulcite and urea is of differential diagnostic importance. These properties are most pronounced in K. pneumoniae.
Toxin formation. For Klebsiella pneumoniae, the ability to produce a heat-stable exotoxin has been established; the toxicity of other species is associated with the action of endotoxin.
Antigenic structure. Klebsiella contains K-antigen (capsular), O-antigen (somatic) and P-antigen (degraded O-antigen).
Resistance. When heated to 60°C, Klebsiella die within 1 hour and are sensitive to the action of chloramine, phenol and other disinfectants. They can be stored at room temperature for several months.
Klebsiella pneumonia. The pathogen was isolated in 1882 by K. Friedlander, which is why it is also called Friedlander’s bacillus. Pathogenic for many animal species: guinea pigs, rabbits, dogs. White mice are especially sensitive to them; when administered subcutaneously or intraperitoneally, sepsis occurs and death occurs within one to two days after infection.
The pathogen causes catarrhal pneumonia in humans, characterized by damage to one or more lobes of the lung in the form of the formation of multiple confluent foci and abscesses. The affected lung tissue contains a large number of Klebsiella and is saturated with mucus. In some cases, pneumobacteria cause meningitis, appendicitis, pyaemia, mastoiditis, cystitis, septicemia (especially in children), sometimes inflammatory diseases of the genitourinary system, and often complicate measles, whooping cough and other infections.
Klebsiella ozena. The pathogen was described in 1893 by R. Abel and causes a fetid runny nose (ozena). Pathogenic for dogs and white mice. In case of intraperitoneal infection with the latter dose
0.5-1 billion microbial bodies die on the second or third day.
The disease in humans is chronic and is expressed in inflammation of the mucous membrane of the nose, pharynx, trachea, larynx, atrophy of the accessory cavities and turbinates, which is clinically manifested by the release of a foul-smelling secretion, which, after drying, forms dense crusts that make breathing difficult. The source of infection is a sick person. The disease occurs in Europe and Asia (India, China, Japan, etc.), mainly among populations living in unfavorable sanitary and hygienic conditions.
Klebsiella rhinoscleroma. The pathogen was first described in 1882 by S. Frisch. Experimentally, rhinoscleroma is reproduced in white mice through intranasal or intraperitoneal infection. During autopsy of dead animals, Klebsiella is found intra- and extracellularly in infectious granulomas formed in internal organs and tissues.
The source of infection is a sick person. The microorganism causes damage to the mucous membrane of the upper respiratory tract, nose, pharynx, larynx, trachea, bronchi with the formation of granulomas and their subsequent sclerosis. Characteristically, the granulation tissue contains giant cells (Mikulich cells), containing clusters of rhinoscleroma rods in the protoplasm. The disease is chronic, with a gradual spread of cartilaginous infiltrates. Death usually occurs as a result of narrowing of the airways.
Immunity. After an illness, low-strength humoral immunity is formed.
Laboratory diagnostics. The detection of capsular bacteria is of diagnostic value for rhinoscleroma and catarrhal pneumonia. In ozena, the presence of specific clinical signs is sufficient to make a diagnosis.
The materials for the study are sputum, nasal mucus, and biopsy samples of granulomatous tissue.
Use bacterioscopy native material, inoculation on weakly alkaline meat peptone or glycerin agar, followed by isolation of a pure culture and its identification by cultural, biochemical, phagolysable and antigenic characteristics.
Among serological methods are used to perform a complement fixation reaction with patient sera and O-antigen, as well as an agglutination reaction with a capsular antigen.
Treatment and prevention. Gentamicin, streptomycin, chloramphenicol, kanamycin, and tetracycline are used for treatment. According to indications, vaccine therapy is carried out using capsular strains of bacteria neutralized by heating.
There are no specific prevention methods. Prevention is achieved by early identification of patients, appropriate treatment and prevention of the possibility of transmission of infection.
Pseudomonas aeruginosa (PSEUDOMONAS AERUGINOSA)
Diseases caused by Pseudomonas aeruginosa are called pyocyanosis. They arise mainly as hospital infections in surgical, burn, urological oncology and other departments as a purulent-inflammatory complication of a wound process or other surgical interventions.
Pseudomonas aeruginosa belongs to the genus Pseudomonas of the Pseudomonaceae family. Among the fairly large number of microorganisms included in the genus Pseudomonas, three species are of greatest importance for medicine and veterinary medicine: Ps. aeruginosa, Ps. mallei (the causative agent of glanders) and Ps. pseudomallei.
Morphology. Pseudomonas aeruginosa is a gram-negative bacterium 1-3 microns long and 0.5-1 microns wide. In smears, individuals of Pseudomonas aeruginosa are located singly, in pairs or in the form of short chains. They are motile, monotrichous, do not form spores, and under certain cultivation conditions they produce a capsule-like substance - extracellular mucus, which surrounds the microbial cell in a thin layer. There are mucoid strains, most often isolated from patients with cystic fibrosis, bronchiectasis, and less often from other lesions of the bronchopulmonary system.
Cultural and enzymatic properties. According to the type of respiration, Pseudomonas aeruginosa is a facultative anaerobes; it grows well on simple nutrient media at a temperature of 30-37°C, but cultivation is also possible at 42°C.
On a liquid nutrient medium it forms a superficially located characteristic film of grayish-silver color. Forms five different types of colonies on meat peptone agar:
flat, irregular shape; small, transparent with rounded, smooth edges; folded (“daisy flower”); mucous membranes; dwarf, or dotted.
The saccharolytic properties of Pseudomonas aeruginosa are weakly expressed and are practically limited to the fermentation of glucose. Proteolytic activity is manifested by the ability to liquefy gelatin, coagulated horse whey, and also hydrolyze casein. The generic characteristic of pseudomonads is the ability to synthesize cytochrome oxidase, and on 5% blood agar - to form zones of hemolysis.
Pigment formation. A characteristic biological feature of the Pseudomonas species, which greatly simplifies the identification of 70-80% of strains, is the ability to synthesize a water-soluble phenazine pigment - pyocyanin, which colors the nutrient medium and patient dressings blue-green. In addition, the vast majority of strains produce the green pigment pyoverdine, which fluoresces in UV rays, and some strains can also produce other pigments - red (pyorubin), black (pyomelanin) or yellow (ά-oxyphenazine).
Antigenic structure. Pseudomonas aeruginosa contains an O-antigen (somatic), which is an endotoxin of a lipopolysaccharide structure, and an H-antigen (flagellar).
Toxin formation. Pseudomonas aeruginosa produces heat-labile exotoxin A, an enterotoxin, and contains endotoxin of lipopolysaccharide nature.
Pathogenicity factors include heat-stable exoenzyme S, hyaluronidase, neuraminidase, hemolysins, extracellular mucus.
Resistance. Pseudomonas aeruginosa is sensitive to drying, the action of chlorine-containing disinfectants and high temperature. It is resistant to iodoform, furatsilin, diocide, and remains viable under anaerobic conditions for up to two weeks.
Epidemiology. Features of the spread and clinical circulation of Pseudomonas aeruginosa correspond to the patterns of epidemiological features of hospital infections.
Pathogenesis and clinic. Pseudomonas aeruginosa exhibits pathogenicity only in a weakened organism, when it enters places with impaired defense mechanisms or when involved in mixed infections. This is observed during contamination of wound and burn surfaces, lumbar puncture, surgical ophthalmological interventions, use of infected respirators or other medical instruments, and catheterization of the urinary tract.
The pathogenesis is based on the development of purulent inflammation, which, depending on the lesion or area of infection, is clinically manifested by meningitis, necrotizing pneumonia, urethrocystitis, pyelonephritis, etc. In children, debilitated or cancer patients, sepsis often develops, resulting in death.
Immunity. With Pseudomonas aeruginosa infection, a weak, short-term humoral and antimicrobial immunity is formed.
Laboratory diagnostics. Bacteriological diagnosis of Pseudomonas aeruginosa infection includes: isolating a pure culture,
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species identification, intraspecific or strain differentiation.
To isolate a pure culture, selective media with furagin, brilliant green, proponide or ethonium and penicillin are used.
Species differentiation is carried out on the basis of a cytochrome oxidase test using a set of NIB (system of indicator papers). To identify non-pigmented and weakly pigmented strains of Pseudomonas aeruginosa, media that enhance pigment formation are used.
Serological diagnostics include methods of two-dimensional immunodiffusion (ID), immunoelectrophoresis (IEF), RPGA, RSK, staging an opsonphagocytic reaction using erythrocytes or latex.
Treatment Pseudomonas aeruginosa infection is carried out with polymyxins B and M, gentamicin, tobramycin, amikacin, carbenicillin, azlocillin, etc. If necessary, vaccine therapy is used with a chemical ribosomal vaccine or a vaccine from the protein component of endotoxin.
Prevention. To prevent the circulation of Pseudomonas aeruginosa, a set of sanitary and anti-epidemic measures developed for hospital infections is used.
CHOLERA VIBRIO
Cholera is an acute quarantine (conventional) intestinal disease characterized by damage to the small intestine and impaired water-salt metabolism due to profuse diarrhea and profuse vomiting.
The causative agent of cholera - Vibrio cholerae, belongs to the Vibrionaceae family and has four biovars: cholerae, el-tor, proteus, albensis. Two of them are pathogenic for humans: Vibrio cholerae biovar cholerae and Vibrio cholerae biovar el-tor.
Vibrio cholerae (the classic causative agent of Asian cholera) was discovered in 1883 by R. Koch and for a long time was considered the only causative agent of cholera. In 1906, F. Gottschlich isolated the biovar el-tor, the causative agent of cholera, from the intestinal contents of pilgrims who died at the E1-Tor quarantine station (Sinai Peninsula).
Cholera-like diseases can occasionally be caused by so-called NAG vibrios (non-agglutinated by typical cholera sera). NAG vibrios are isolated from water, marine crustaceans and other objects. In terms of morphological and biochemical properties, these vibrios do not differ from true cholera vibrios.
Morphology and tinctorial properties. Vibrio cholerae is a short, comma-shaped rod 1.5-3 microns long. Biovar el-tor is somewhat shorter and thicker. Under the influence of a bacteriophage and in old cultures, the vibrio takes on spiral, spherical and other forms. It does not form spores or capsules; it has a polarly located flagellum (monotrich), which determines the pronounced motility of the vibrio.
It stains well with aniline dyes and is gram-negative.
Cultural properties. According to the type of respiration, Vibrio cholerae is an aerobic or facultative anaerobe, the optimal growth temperature is 37°C. Grows well on low-nutrient media (1% alkaline peptone water, alkaline agar). Demanding on the pH of the environment (from 7.6 to 9.2). In liquid media, after 6-8 hours it forms turbidity and a delicate bluish film; on agar after 12-14 hours - transparent colonies, opalescent in transmitted light. Aronson, Monsur, TSVS media are selective for Vibrio cholerae.
Enzymatic properties. Vibrio cholerae has powerful enzyme systems. Decomposes sucrose, maltose, mannitol, mannose, glucose, lactose to acid (without gas). The relationship to three sugars is characteristic: the decomposition of mannose and sucrose and the lack of decomposition of arabinose. Proteolytic activity is expressed in the ability to liquefy gelatin, hydrolyze casein, form indole, and reduce nitrates to nitrites. Does not form hydrogen sulfide.
Antigenic structure. The causative agent of cholera has two antigens: the heat-stable somatic O-antigen and the heat-labile flagellar H-antigen. The latter is common to the entire genus Vibrio. O-antigen is species- and type-specific. Based on the O-antigen, vibrios are divided into several serological groups. V. cholerae biovar cholerae and biovar el-tor belong to the 01 serological group (agglutinated by the 01 agglutinating serum), the 01 antigen is represented by three components (A, B, C), the different combination of which determines the presence of three serovars of Vibrio cholerae: Inaba, Ogawa, Gikoshima. These serological variants are observed in both classical Vibrio and el-tor.
Virulence factors. Vibrio cholerae produces two types of toxins - endotoxin and exotoxin. Endotoxin has a lipopolysaccharide nature, is released during the destruction of vibrios and contributes to the formation of antibacterial immunity.
Exotoxin (cholerogen) has an enterotoxic effect; it plays a major role in dehydration of the body. Vibrio cholerae produces pathogenicity enzymes - gya-
luronidase, lecithinase, fibrinolysin, plasmacoagulase, collagenase.
Resistance. Vibrio cholerae tolerates low temperatures and freezing well. It persists in ice for several months, in sea and river water for several weeks. In the water of surface reservoirs, silt, and the body of some hydrobionts in the warm season, not only long-term preservation, but also reproduction of vibrio is possible. Survives well in sewage. Boiling kills it within one minute; it quickly dies under the influence of sunlight and drying.
The causative agent of cholera is sensitive even to weak concentrations of sulfuric and hydrochloric acids, as well as to disinfectants. El-tor vibrios are more stable.
Epidemiology. Cholera is an anthroponotic disease. The source of infection is only a person sick with various clinical forms of cholera and a vibrio carrier. The transmission mechanism is fecal-oral. The ways of spreading the infection are water, nutritional, contact and household. The leading route of transmission is water.
Cholera belongs to the group of quarantine infections and can become epidemics and pandemics. Humanity has experienced six cholera pandemics caused by Vibrio cholerae (classic). Since 1961, cholera el-tor has spread, causing the seventh pandemic. Features of cholera caused by the el-tor biovar are the possibility of long-term vibrio carriage and the often occurring erased forms of the disease.
Pathogenesis. Cholera is transmitted through the mouth. Once in the stomach, some of the cholera vibrios die in its acidic environment, releasing endotoxin. Having penetrated into the small intestine, where there is an alkaline environment and an abundance of protein breakdown products (peptones), vibrios actively multiply, releasing an exotoxin (cholerogen) and the so-called permeability factor, which plays a certain role in disrupting the permeability of blood vessels and cell membranes of the intestinal wall. Under the influence of cholerogens, the enzyme adenyl cyclase is activated in the epithelial cells of the small intestine, which enhances the synthesis of adenosine monophosphate, leading to increased secretion of electrolytes and water from the cell into the intestinal lumen. As a result of this, the mucous membrane of the small intestine begins to secrete a huge amount of isotonic fluid, which the large intestine does not have time to absorb. This causes profuse diarrhea. Loss of fluid also occurs due to excessive vomiting. The daily volume of feces and vomit can reach 10 liters or more. Such a significant loss of fluid and salts by the body leads to thickening of the blood, increasing its viscosity
a decrease in the volume of circulating blood, an increase in hemodynamic disorders, disruption of tissue metabolic processes with the development of acidosis and tissue hypoxia. Due to severe dehydration, urination stops, which, in turn, causes uremic phenomena. Improper treatment or lack of it leads to the development of acute renal failure and hypokalemia. The latter, in turn, can cause intestinal atony, hypotension, arrhythmia, and changes in the myocardium.
Clinic. The incubation period ranges from several hours to five days (usually two or three). The clinical picture is very diverse - from the mildest manifestations of enteritis to the most severe forms, occurring with severe dehydration and ending in death on the 12th day of the disease.
The degree of dehydration determines the various clinical forms of cholera: mild, moderate, severe and very severe (algic). The mild form is characterized by dehydration of the first degree: loose stools and vomiting in patients appear no more than five times a day, the total loss of fluid does not exceed 3% of body weight. Such patients feel satisfactory; complaints are reduced to a feeling of weakness, dry mouth, and thirst.
Cholera of moderate severity is caused by dehydration of the second degree (fluid loss is up to 6% of body weight): an acute onset with the appearance of loose stools, which become more frequent up to 15-20 times a day, gradually loses its fecal character and takes on the appearance of rice water. The diarrhea is accompanied by profuse vomiting. The phenomena of dehydration quickly increase: the skin is dry and pale, cold to the touch, its turgor is reduced. Short-term cramps of the calf and chewing muscles, muscles of the hands, and feet appear. There is cyanosis of the lips and fingers, and hoarseness of the voice.
Severe form of cholera is characterized by third degree dehydration (fluid loss is up to 9% of body weight): the development of all symptoms of dehydration in the first 10-12 hours of illness. Weakness, cyanosis of the skin quickly increases, and facial features become sharper.
IV degree dehydration (fluid loss reaches 10% of body weight or more) corresponds to the most severe form of cholera (algic form): the skin is folded and does not straighten (“washerwoman’s hands”), the voice is silent, the eyeballs are sunken, blood pressure is low. , body temperature - 35-34.5 °C. Diuresis decreases sharply, diarrhea and vomiting stop, the patient loses consciousness, and cholera coma develops.
The most severe forms of the disease include dry and fulminant cholera. Dry begins suddenly with symptoms of severe intoxication and increased body temperature. There is no vomiting or diarrhea. Rigidity of various muscle groups appears,
Cardiovascular weakness develops. The outcome of this form of the disease is often fatal. Fulminant cholera occurs in almost the same way, in which, in addition to severe general manifestations, severe intestinal disorders occur.
In some patients, during convalescence, the temperature suddenly rises, headache, anxiety, and delirium appear. An extremely serious complication develops - cholera typhoid, in the pathogenesis of which increased permeability of the intestinal mucosa and activation of normal microflora play a role.
Immunity. After an illness, strong immunity remains.
Laboratory diagnostics. The main method of laboratory diagnosis of cholera is bacteriological. The materials for the study are feces, vomit, sectional material, as well as water and food products. Due to the fact that cholera is a particularly dangerous infection, studies are carried out in specialized laboratories.
Diagnosis of cholera is carried out in stages:
1. Smears are prepared from stool and stained with Gram and diluted fuchsin. The smears reveal curved rods arranged in the shape of schools of fish.
2. The test material is inoculated on 1% alkaline peptone water and alkaline agar to isolate a pure culture.
3. The isolated culture is identified by: morphological characteristics (in a smear); mobility in the hanging drop preparation; enzymatic properties on Hiss media (no fermentation of arabinose), on meat-peptone gelatin (funnel-shaped liquefaction) and nitrosoindole test (pink color due to the appearance of nitrosoindole under the influence of Vibrio cholerae); antigenic properties in the agglutination reaction with 01 agglutinating serum.
4. To differentiate the V. cholerae biovar and the el-tor biovar, the hemolytic properties of the isolated culture are examined and its sensitivity to polymyxin and bacteriophages is determined. Biovar V. cholerae does not hemolyze sheep erythrocytes and is sensitive to polymyxin and bacteriophage C Mukherjee type four.
Biovar el-tor causes hemolysis of sheep erythrocytes, is resistant to polymyxin, and is lysed by bacteriophage el-tor II.
The final conclusion about the isolated culture is issued after 36-48 hours.
Used for retrospective diagnosis serological method - agglutination reaction and indirect hemagglutination reaction. Accelerated diagnostic methods: immunofluorescence; immobilization of O1 vibrios with cholera serum.
Treatment. The main goals of therapy for cholera are restoration of circulating blood volume, electrolyte composition of blood, tissues and exposure to the pathogen.
In case of moderate cholera, restoration of water-salt balance is carried out by oral administration of glucose-salt solutions "Regidron", "Oralit". In severe forms, polyionic solutions “Disol”, “Trisol”, “Kvartasol”, “Acesol”, “Chlosol” are administered intravenously.
After the cessation of vomiting, along with rehydration, etiotropic therapy is carried out by prescribing tetracycline or chloramphenicol.
Prevention cholera includes the protection of state borders from the possibility of penetration of the disease and a set of anti-epidemic measures: identification of patients and vibration carriers, their isolation, treatment, sanitation; water supply supervision; combating water pollution; sanitary education work, etc.
For specific prevention, the population is vaccinated according to epidemiological indications with cholera toxoid in combination with the O-antigen of Vibrio cholerae.
Related information.
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Shigella
Bacteria of the genus Shigella are the causative agents of bacterial dysentery, or shigellosis. Dysentery is a polyetiological disease. It is caused by various types of bacteria, named Shigella in honor of A. Shiga. They are currently classified in the genus Schigella, which is divided into four species. Three of them - S. dysenteriae, S. flexneri and S. boydii - are divided into serovars, and S. flexneri is also divided into subserovars.Morphology and physiology
In their morphological properties, Shigella differs little from Escherichia and Salmonella. However, they lack flagella and are therefore nonmotile bacteria. Many strains of Shigella have pili. Different kinds Shigella are identical in their morphological properties. The causative agents of dysentery are chemoorganotrophs, undemanding to nutrient media. On solid media, when isolated from a patient’s body, S-form colonies are usually formed. Shigella species Schigella sonnei form two types of colonies - S-form (I phase) and R-form (II phase). When subcultured, phase I bacteria form both types of colonies. Shigella is less enzymatically active than other enterobacteria: when fermenting glucose and other carbohydrates, they form acidic products without gas formation. Shigella does not break down lactose and sucrose, with the exception of S. sonnei, which slowly (on the second day) breaks down these sugars. It is impossible to distinguish the first three species based on biochemical characteristics.Antigens
Shigella, like Escherichia and Salmonella, have a complex antigenic structure. Their cell walls contain O-, and in some species (Shigella Flexner) also K-antigens. Their chemical structure is similar to Escherichia antigens. The differences lie mainly in the structure of the terminal links of LPS, which determine the immunochemical specificity, which makes it possible to differentiate them from other enterobacteria and among themselves. In addition, Shigella has cross-antigenic relationships with many serogroups of enteropathogenic Escherichia, which mainly cause dysentery-like diseases, and with other enterobacteria.Pathogenicity and pathogenesis
The virulence of Shigella is determined by their adhesive properties. They adhere to colon enterocytes due to their microcapsule. Then they penetrate enterocytes with the help of mucinase, an enzyme that destroys mucin. After colonizing enterocytes, Shigella enters the submucosal layer, where it is phagocytosed by macrophages. In this case, the death of macrophages occurs and a large number of cytokines are released, which, together with leukocytes, cause an inflammatory process in the submucosal layer. As a result, intercellular contacts are disrupted and a large number of Shigella penetrate into the enterocytes activated by them, where they multiply and spread to neighboring cells without exiting into the external environment. This leads to destruction of the epithelium of the mucous membrane and the development of ulcerative colitis. Shigella produces an enterotoxin, the mechanism of action of which is similar to the heat-labile enterotoxin of Escherichia. Shigella Shiga produces a cytotoxin that attacks enterocytes, neurons, and myocardial cells. This indicates the presence of three types of activity - enterotoxic, neurotoxic and cytotoxic. At the same time, when Shigella is destroyed, endotoxin is released - LPS of the cell wall, which enters the blood and has an effect on the nervous and vascular systems. All information about the pathogenicity factors of Shigella is encoded in a giant plasmid, and the synthesis of Shiga toxin is encoded in a chromosomal gene. Thus, the pathogenesis of dysentery is determined by the adhesive properties of pathogens, their penetration into the enterocytes of the colon, intracellular reproduction and production of toxins.Immunity
With dysentery, local and general immunity develops. In local immunity, secretory IgA (SIgA), which is formed in the 1st week of the disease in the lymphoid cells of the intestinal mucosa, is essential. By covering the intestinal mucosa, these antibodies prevent the attachment and penetration of Shigella into epithelial cells. In addition, during the infection, the titer of serum antibodies IgM, IgA, IgG increases, which reaches a maximum in the 2nd week of the disease. The largest amount of IgM is detected in the 1st week of illness. The presence of specific serum antibodies is not an indicator of the strength of local immunity.Ecology and epidemiology
The habitat of Shigella is the human colon, in the enterocytes of which they multiply. The source of infection is patients, people and bacteria carriers. Infection occurs by ingesting contaminated food or water. Thus, the main route of transmission of infection is nutritional. However, cases of contact-household transmission have been described. Resistance different types Shigella is not the same to environmental factors - S. dysenteriae is the most sensitive, S. sonnei is the least sensitive, especially in the R-form. They remain in feces for no more than 6-10 hours.Dysentery (shigellosis)
Dysentery is an acute or chronic infectious disease characterized by diarrhea, damage to the mucous membrane of the colon and intoxication of the body. This is one of the most common intestinal diseases in the world. It is caused by various types of bacteria of the genus Shigella: S.dysenteriae, S.flexneri, S.boydii, S.sonnei. In the post-war years in industrialized countries, dysentery is more often caused by S.flexneri and S.sonne. In Ukraine, an international classification of these bacteria is used, which takes into account their biochemical properties and features of the antigenic structure. There are 44 serovars of Shigella in total. The main method of microbiological diagnosis of dysentery is bacteriological. The pathogen isolation scheme is classical: inoculation of the material on enrichment medium and Ploskirev agar, obtaining a pure culture, studying its biochemical properties and identification using polyvalent and monovalent agglutinating sera.Taking material for research
A positive result of a microbiological analysis largely depends on the timely and correct collection of the test material. In all cases and bacteria, they often take stool, less often - vomit and lavage water from the stomach and intestines. Feces (1-2 g) are taken with a glass rod from a bedpan or diaper, including pieces of mucus and pus (but not blood). It is best to take mucus (pus) from the affected areas of the mucous membrane during a colonoscopy for examination. When collecting and cultivating material, it is important to strictly adhere to certain rules. Bacteriological research, if possible, should begin before the start of etiotropic treatment. Before collecting feces, dishes (vessels, pots, jars) are scalded with boiling water and under no circumstances treated with disinfectant solutions. Shigella is very sensitive. The material under study must be quickly (at the patient’s bedside) sown in the enrichment medium and, in parallel, on selective agar in a Petri dish. The stool can be collected without waiting for a bowel movement using a cotton swab or Ziemann rectal tubes. The collected material or inoculated media must be immediately delivered to the laboratory. If it is impossible to culture in the hospital and quickly deliver the stool, they are kept in a preservative (30% glycerol + 70% phosphate buffer) at 4-6 ° C for no more than a day. Dysentery pathogens very rarely penetrate into the blood and urine, and therefore these objects are usually not sow Bacteriological analysis of sectional material must be carried out as soon as possible after death (large intestine, mesenteric lymph nodes, pieces of parenchymal organs). During outbreaks of dysentery, food products are also examined, especially milk, cheese, and sour cream.Bacteriological research
Inoculation of feces is carried out in parallel on Ploskirev’s selective medium to obtain isolated colonies and always in selenite broth in order to accumulate Shigella, if there are few of them in the material being studied. Mucopurulent pieces are selected with a bacteriological loop, thoroughly rinsed in 2-3 test tubes with an isotonic sodium chloride solution, applied to Ploskirev’s medium and rubbed into agar in a small area with a glass spatula. Then the spatula is removed from the medium and the residual material is rubbed dry onto the remaining uninoculated surface. When sowing in 2-3 cups, a new portion of seed is applied to each of them. Pieces of mucus and pus are sown into selenite broth without rinsing. In the absence of mucopurulent pieces, feces are emulsified in 5-10 ml of 0.85% sodium chloride solution and 1-2 drops of the supernatant are sown on Ploskirev’s medium. Non-emulsified stools are sown in selenite broth in a ratio of 1:5. When inoculating vomit and rinsing water, selenite broth of double concentration is used and the ratio of inoculum to medium is 1:1. Culture media inoculated at the patient's bedside are directly placed into the thermostat. All crops are grown at 37 ° C for 18-20 hours. On the second day, with the naked eye or using a 5x-10x magnifying glass, examine the growth pattern on Ploskirev’s medium, where Shigella forms small, transparent, colorless columns. Shigella Sonne can produce columns of two types: some are flat with jagged edges, others are round, convex, with a damp sheen. 3-4 colonies are microscopically examined, everything is destroyed and replanted on the Olkenitsky center to isolate a pure culture. If there is no growth on Ploskirev agar, or there are no characteristic Shigella colonies, sow from selenite broth onto Ploskirev or Endo agar. If there are a sufficient number of typical colonies, an approximate agglutination reaction is performed on glass with a mixture of Flexner and Sonne sera. On the third day, the growth pattern on Olkenitsky’s medium is taken into account. Shigels cause characteristic changes in three-part agar (the column turns yellow, the color of the slanted particle does not change, there is no blackening). A suspicious culture is sown in Hiss medium to determine biochemical properties, or enterotests are used. Serological identification of isolated cultures is carried out using a glass agglutination reaction, first with a mixture of sera against Flexner and Sonne species, which are often found, and then with monospecies and monoreceptor sera. IN Lately They produce commercial polyvalent and monovalent sera against all types of dysentery pathogens. A coaglutination reaction is also used to determine the type of Shigella. The type of pathogen is determined by a positive reaction with protein A of Staphylococcus aureus, on which specific antibodies against Shigella are adsorbed. A drop of antibody-sensitized protein A is applied to a typical colony, the dish is shaken, and after 15 minutes the appearance of aglutinate is observed under a microscope. The coaglutination reaction can be performed already on the second day of the study if there is a sufficient number of lactose-negative colonies in the medium. In order to quickly and reliably identify Shigella, direct and indirect reactions of immunofluorescence and enzyme antibodies are also performed. The latter in dysentery is highly specific and is increasingly used in laboratory diagnosis of the disease. To detect antigens in the blood of patients, including as part of circulating immune complexes, the hemagglutination aggregate reaction and the ELISA method (Shigelaplast diagnostic test system) can be used. Shigella antigens in feces and urine are detected using RNGA, RSK and coaglutination. These methods are highly effective, specific and suitable for early diagnosis. To establish whether the isolated cultures belong to the genus Shigella, a keratonic test is also performed on Guinea pigs. A loop of agar culture or a drop of broth is inserted into the conjunctival sac. It is important not to injure the cornea. New Shigella infections cause severe keratitis 2-5 days after the introduction of the culture. Salmonella can also cause conjunctivitis, but it does not affect the cornea. However, it should be remembered that enteroinvasive Escherichia coli (EIEC), especially serovars 028, 029, 0124, 0143, etc., also cause experimental keratoconjunctivitis in Guinea pigs. The bacteriological method for diagnosing dysentery is reliable, but in different laboratories (depending on the qualifications of bacteriologists and laboratory technicians) it gives only 50-70% positive results. In addition to diagnosing diseases, bacteriological testing is also carried out to identify bacteria carriers, especially among employees of food enterprises, child care institutions and medical institutions. In order to identify the sources of infection, Shigella phagovars and colicinovars are determined.Serological diagnosis
Serological diagnosis of dysentery is rarely performed. The infectious process is not accompanied by significant antigenic irritation, therefore antibody titers in the serum of patients and convalescents are low. they are detected on days 5-8 of the disease. More antibodies are formed in the 2-3rd week. Volumetric agglutination reaction with microbial diagnostics is performed in the same way as the Widal reaction for typhoid fever and paratyphoid fever. Blood serum is diluted from 1:50 to 1:800. The diagnostic titer of antibodies to S.flexneri in adult patients is considered to be 1:200, in S.dysenteriae and S.sonnei - 1:100 (in children, respectively - 1:100 and 1:50).More reliable results obtained when staging RNGA, especially when using the method of paired sera. An increase in titer of 4 or more times has diagnostic significance. Erythrocyte diagnosticums are made mainly from S.flexneri and S.sonnei antigens. An allergic intradermal test with Tsuverkalov’s dysenterin (a solution of protein fractions of Shigella Flexner and Sonne) is also of auxiliary value for diagnosis. It becomes positive in patients with dysentery starting from the 4th day. The reaction is recorded after 24 hours. When hyperemia and swelling of the skin with a diameter of 35 mm or more appears, the reaction is assessed as strongly positive, at 20-34 mm - moderate and at 10-15 mm - doubtful.Specific prevention and treatment
The receipt of various vaccines (heated, formalinized, chemical) did not solve the problem of specific prevention of dysentery, since they all had low effectiveness. Fluoroquinolones and, less commonly, antibiotics are used for treatment.Bacteria of the genus Shigella are the causative agents of bacterial dysentery, or shigellosis. Dysentery is a polyetiological disease. It is caused by various types of bacteria, named Shigella in honor of A. Shiga. They are currently classified in the genus Schigella, which is divided into four species. Three of them - S. dysenteriae, S. flexneri and S. boydii - are divided into serovars, and S. flexneri is also divided into subserovars.
Morphology and physiology. In their morphological properties, Shigella differs little from Escherichia and Salmonella. However, they lack flagella and are therefore nonmotile bacteria. Many strains of Shigella have pili. Different types of Shigella are identical in their morphological properties. The causative agents of dysentery are chemoorganotrophs, undemanding to nutrient media. On solid media, when isolated from a patient’s body, S-form colonies are usually formed. Shigella species Schigella sonnei form two types of colonies - S-form (I phase) and R-form (II phase). When subcultured, phase I bacteria form both types of colonies. Shigella is less enzymatically active than other enterobacteria: when fermenting glucose and other carbohydrates, they form acidic products without gas formation. Shigella does not break down lactose and sucrose, with the exception of S. sonnei, which slowly (on the second day) breaks down these sugars. It is impossible to distinguish the first three species based on biochemical characteristics.
Antigens. Shigella, like Escherichia and Salmonella, have a complex antigenic structure. Their cell walls contain O-, and in some species (Shigella Flexner) also K-antigens. Their chemical structure is similar to Escherichia antigens. The differences lie mainly in the structure of the terminal links of LPS, which determine the immunochemical specificity, which makes it possible to differentiate them from other enterobacteria and among themselves. In addition, Shigella has cross-antigenic relationships with many serogroups of enteropathogenic Escherichia, which mainly cause dysentery-like diseases, and with other enterobacteria.
Pathogenicity and pathogenesis. The virulence of Shigella is determined by their adhesive properties. They adhere to colon enterocytes due to their microcapsule. Then they penetrate enterocytes with the help of mucinase, an enzyme that destroys mucin. After colonizing enterocytes, Shigella enters the submucosal layer, where it is phagocytosed by macrophages. In this case, the death of macrophages occurs and a large number of cytokines are released, which, together with leukocytes, cause an inflammatory process in the submucosal layer. As a result, intercellular contacts are disrupted and a large number of Shigella penetrate into the enterocytes activated by them, where they multiply and spread to neighboring cells without exiting into the external environment. This leads to destruction of the epithelium of the mucous membrane and the development of ulcerative colitis. Shigella produces an enterotoxin, the mechanism of action of which is similar to the heat-labile enterotoxin of Escherichia. Shigella Shiga produces a cytotoxin that attacks enterocytes, neurons, and myocardial cells. This indicates the presence of three types of activity - enterotoxic, neurotoxic and cytotoxic. At the same time, when Shigella is destroyed, endotoxin is released - LPS of the cell wall, which enters the blood and has an effect on the nervous and vascular systems. All information about the pathogenicity factors of Shigella is encoded in a giant plasmid, and the synthesis of Shiga toxin is encoded in a chromosomal gene. Thus, the pathogenesis of dysentery is determined by the adhesive properties of pathogens, their penetration into the enterocytes of the colon, intracellular reproduction and production of toxins.
Shigella |
Immunity. With dysentery, local and general immunity develops. In local immunity, secretory IgA (SIgA), which is formed in the 1st week of the disease in the lymphoid cells of the intestinal mucosa, is essential. By covering the intestinal mucosa, these antibodies prevent the attachment and penetration of Shigella into epithelial cells. In addition, during the infection, the titer of serum antibodies IgM, IgA, IgG increases, which reaches a maximum in the 2nd week of the disease. The largest amount of IgM is detected in the 1st week of illness. The presence of specific serum antibodies is not an indicator of the strength of local immunity.
Ecology and epidemiology. The habitat of Shigella is the human colon, in the enterocytes of which they multiply. The source of infection is patients, people and bacteria carriers. Infection occurs by ingesting contaminated food or water. Thus, the main route of transmission of infection is nutritional. However, cases of contact-household transmission have been described. The resistance of different types of Shigella to environmental factors is not the same - S. dysenteriae is the most sensitive, S. sonnei is the least sensitive, especially in the R-form. They remain in feces for no more than 6-10 hours.
Laboratory diagnostics. A pure culture of the pathogen is isolated by inoculating the patient’s feces on a differential diagnostic nutrient medium (Ploskirev’s, Levin’s, etc.) medium, followed by its identification on a variegated series of media and by antigenic properties in an agglutination reaction to determine the species and serovar. The percentage of positive results is quite low, especially in chronic dysentery.
Specific prevention and treatment. The receipt of various vaccines (heated, formalinized, chemical) did not solve the problem of specific prevention of dysentery, since they all had low effectiveness. Fluoroquinolones and, less commonly, antibiotics are used for treatment.
Shigella in a microscopic specimen of stool from a patient with bacillary dysentery
Shigella (lat. shigella) is a genus of gram-negative, facultative anaerobic bacteria that are causative agents of dysentery.
Shigella classification
The genus Shigella (Latin: shigella) is included in the family of enterobacteria (Latin: enterobacteriaceae), the order of enterobacteria (Latin: enterobacteriales), the class of gamma-proteobacteria (Latin: γ proteobacteria), the type of proteobacteria (Latin: proteobacteria), the kingdom of bacteria.
The Shigella genus includes 4 species corresponding to four serogroups:
Shigella dysenteriae, serogroup A, includes 12 serotypes
Shigella flexneri, serogroup B - 6 serotypes
Shigella Boyd (lat. shigella boydii), serogroup C - 23 serotypes
Shigella sonnei, serogroup D - serotype 1
Shigella. General information
Shigella have the appearance of rods without flagella, with rounded ends measuring 2-3 by 0.5-0.7 microns. They do not form spores or capsules. Shigella is poorly resistant to physical, chemical and biological environmental factors. Shigella lives in water, soil, food, on objects, dishes, vegetables, and fruits for 5–14 days. At a temperature of 60 °C, Shigella die in 10–20 minutes, at 100 °C - instantly. Direct sunlight kills Shigella within 30 minutes. In the absence of sunlight, high humidity and moderate temperatures, Shigella remains viable in the soil for up to 3 months. Shigella can survive in gastric juice for only a few minutes. In stool samples, Shigella die from the acidic reaction of the environment and antagonist bacteria after 6–10 hours. In dried or frozen stool, Shigella is viable for several months.
The most resistant to external influences is the Shigella species shigella sonnei, the least resistant is shigella dysenteriae.
Shigella is named after the Japanese physician and microbiologist Kiyoshi Shiga (or Shiga; 1871–1951), who in 1897 isolated the bacteria in its pure form, today classified as shigella dysenteriae.
Shigella - the causative agent of dysentery All types of Shigella can be the causative agents of an infectious disease - bacterial dysentery (also called shigellosis), which occurs with symptoms of intoxication and predominantly affects the distal part of the colon. The most favorable conditions for the development of Shigella are in the transverse colon and descending colon.
Infection occurs through the fecal-oral or household contact route, through water and food products. Shigellosis can be transmitted by flies and cockroaches.
Shigellosis is characterized by constant dull pain throughout the abdomen, which later becomes acute cramping, localized in the lower abdomen, usually on the left or above the pubis. During the act of defecation, nagging pain in the rectal area, radiating to the sacrum. Initially, frequent bowel movements - up to 10–25 per day, mainly from mucus with inclusions of blood, and in a later period, admixtures of pus. False urge to defecate - tenesmus - is frequent.
Bacterial dysentery (shigellosis) has incubation period from several hours to 7 days, most often occurs acutely and is manifested by malaise, chills, headache, fever, convulsions, single or repeated vomiting. The patient's temperature rises. At the same time or slightly later, abdominal pain appears. Full recovery occurs in 2–3 weeks. In some patients, dysentery becomes chronic.
In the United States, Shigella is the third (after Salmonella and Campylobacter) cause of foodborne illnesses and hospitalizations. In 2010, there were a total of 1,780 cases of shigellosis reported in the United States. 333 sick people were hospitalized. However, fatal shigellosis, unlike a number of other food infections, has not been recorded.
as the antibiotic of choice - ciprofloxacin 500 mg twice a day for adults, 15 mg per kg of body weight twice a day for children, taken for three days
as alternative antibacterial agents:
pivmecillin 400 mg 4 times a day for adults, 20 mg per kg of body weight twice a day for children, taken for five days or
ceftriaxone - in children 50-100 mg per kg of body weight intramuscularly for 2-5 days
When choosing an antibiotic, take into account the results of drug sensitivity studies of Shigella strains recently isolated in a particular area.
Antibiotics active against Shigella Antibacterial agents (those described in this reference book) active against Shigella: rifaximin, furazolidone, nifuroxazide, ciprofloxacin. Josamycin is active against some species of Shigella. Nifuratel is active against shigella flexneri and shigella sonnei.
Shigella (lat. Shigella) is a genus of gram-negative rod-shaped bacteria that does not form spores. They are close in origin to Escherichia coli and Salmonella. For humans and primates they are causative agents of diseases from the shigellosis group.
Divided into four serogroups
Serogroup A: S. dysenteriae (15 serotypes (serotype 1 produces Shiga toxin))
Serogroup B: S. flexneri (8 serotypes and 9 subtypes)
Serogroup C: S. boydii (19 serotypes)
Serogroup D: S. sonnei (1 serotype)
Bacteria of the genus Shigella cause a number of intestinal infectious diseases in humans, collectively called shigellosis (shigellosis). An equally common term for these diseases is “bacterial dysentery” or simply dysentery.
The disease occurs when bacteria of the genus Shigella enter the human body, penetrate the intestinal tract, where they attach to the epithelium of the distal colon, after which they begin to multiply rapidly. This leads, on the one hand, to damage to intestinal tissue. On the other hand, Shigella bacteria secrete endotoxins, and Shigella Grigoriev-Shiga produces an exotoxin, also called Shigatoxin (similar to the verotoxin secreted by enterohemorrhagic E. coli), which causes intoxication of the body, sometimes quite severe. Dysenteric toxins act on the walls of blood vessels, the central nervous system, peripheral nerve ganglia, the sympathetic-adrenal system, the liver, and the circulatory organs.
The disease can occur in acute and chronic form. Acute dysentery is characterized by fever, abdominal pain, diarrhea with blood and mucus. The severity of the disease is largely determined by the type of pathogen. The most severe forms are observed with dysentery caused by Grigoriev-Shiga and Flexner bacteria. In severe forms of dysentery, patients may even die from infectious-toxic shock
The incubation period ranges from 1 to 7 days, more often 2-3 days.
Carriers and distribution Shigellosis is a widespread infectious disease that accounts for a significant portion of acute intestinal infections worldwide. According to the FDA (U.S. Food & Drug Administration), up to 140 million people worldwide suffer from shigellosis every year. Mostly people in underdeveloped countries get sick. In these regions, dysentery caused by Shigella Flexnera predominates, which is associated with the predominantly water and household transmission of the pathogen in conditions of an extremely low level of sanitary and communal amenities. In economically developed countries, Sonne dysentery dominates, which is characterized by food transmission in conditions of a high level of centralization of public catering and food supply to the population. The incidence rate in developed countries is much lower. Thus, in the United States, the incidence of shigellosis does not exceed 300 thousand people per year (about 10% of all registered intestinal diseases). In Russia in 1997, the number of shigellosis diseases did not exceed 100 thousand people (estimate based on an article from the journal "Attending Doctor" No. 7/99).
The mechanism of transmission of the pathogen is fecal-oral. Routes of transmission - through water contaminated with fecal waste, food (through contaminated food products, especially milk and dairy products, raw vegetables, various salads are also dangerous) and household (dirty hands, dishes, toys, etc.). Shigellosis spreads quite easily through direct contact with the bacteria carrier due to the extremely low infectious dose (about 10 bacteria are enough for infection).
Danger to humans Shigellosis (bacterial dysentery) is dangerous for all people, but it especially affects the elderly, people with weakened bodies (shigellosis is especially common in AIDS patients), as well as children. Moreover, dysentery rarely affects children under 6 months; the most “sensitive” age is 2-3 years. Severe dysentery occurs in 3-5% of cases. It occurs with high fever or, conversely, with hypothermia. There is severe weakness, adynamia, and there is a complete absence of appetite. Patients are lethargic, apathetic, pale skin, rapid pulse, weak filling. A picture of infectious collapse may develop. Stools up to 50 times a day, mucous-bloody.
The mortality rate from dysentery when infected with Shigella dysenteriae 1 (Shigella Grigoriev-Shiga) and Shigella flexneri 2a (Flexner's dysentery) can be up to 10-15%.
Pathogenic bacteria from the genus Escherichia cause both diarrheal and parenteral forms of Escherichiosis. In the clinic, meningitis, pyelitis, otitis, pneumonia, surgical wound infection and other purulent-inflammatory lesions caused by Escherichia are often encountered.
The type species is E.coli. Based on the presence of 0 and K antigens, this species is divided into serogroups and further into many serovars that differ in the H antigen. The nomenclature of Escherichia is carried out according to antigenic formulas with the designation of serial numbers of 0-, K- and H-antigens. For example, E. coli 0124, K72 (B17), N-.
Escherichia are short, polymorphic gram-negative rods that do not form spores. Many serovars have a microcapsule and pili (adhesive and sexual) and are motile. In terms of morphological, enzymatic and cultural properties, pathogenic and non-pathogenic varieties of Escherichia do not differ from each other. Moreover, Escherichia of different serovars may have the same or unequal biological properties. On media they grow most often in the form of S-forms, less often rough (R) forms. Lactose-negative Escherichia on differential-selective media for the isolation (isolation) of enterobacteria form colonies similar to those of Shigella.
Escherichia catabolizes carbohydrates (with or without gas). Many reactions are variable. Bacteria of this genus do not hydrolyze gelatin, do not exhibit urease and lipase activity, and do not utilize sodium citrate and malonate. Usually grow on acetate medium, decarboxylate lysine, give a positive reaction with methyl-rot and negative with acetoin. Escherichia do not produce hydrogen sulfide. Although cases of isolation of E. coli H2S+ from humans, domestic animals and from environmental objects have been described (cited from Zaslavsky B.A. et al., 1986).
Many serovars produce indole. The most informative tests for assigning a culture to the genus Escherichia are: Simmons citrate, urea, malonate, sodium acetate, hydrogen sulfide production, phenylalanine test, lysine decarboxylation and motility.
E.coli and all Shigella form one genospecies, in which Shigella form a biogroup of metabolically inactive, nonmotile microorganisms. Metabolically inactive strains of E. coli are difficult to distinguish from Shigella.
This especially applies to the biogroup consisting of lactose-negative, immobile and non-gas-forming Escherichia when fermenting carbohydrates. Another biogroup is characterized by the absence of active lysine, arginine and ornithine decarboxylases.
There are also strains that show atypical reactions in various tests (citrate, adonite, inositol, indole and others). Therefore, it is recommended to determine the entire biochemical profile during identification, and not just “key” tests.
Table 12. Distinctive features of bacteria of the genus Escherichia
The antigenic structure of Escherichia is very complex. For practical purposes (construction of antigen diagnostic schemes, serological identification), the most important are the O-H and K antigens. In mucous forms of Escherichia, a thermolabile M-antigen is found, similar to the M-antigen of Salmonella. It prevents agglutinability in OK sera. Some fimbrial antigens of Escherichia are related to the corresponding antigens of Shigella (Flexner's species), which is associated with the frequent agglutinability of Escherichia in Shigella sera.
Escherichia 0 antigen is a specific lipopolysaccharide protein complex. Therefore, the antigen is distinguished into 173 0-serogroups. 0-antigens vary in the composition of monosaccharides and structures. To prepare the antigen, when performing the 0-agglutination reaction, the culture is heated at 1000C for an hour. Within the serological group, the factor composition of 0-antigens has been identified: the general factor is designated by the symbol “a”, additional ones - “b”, “c”, etc. For example, E. coli O112 av and O112 ac. Escherichia are related to other genera of bacteria, in particular Shigella, Salmonella, and Klebsiella. For example, the O1 antigen of Escherichia is identical to the O antigen of Shigella Flexner serovars 1,4,2 and 4a, as well as serovar 1 of S.dysenteriae and serovar O-42 of Salmonella.
The polyagglutinability of heated Escherichia cultures in O-sera may also be associated with the occasional presence of antibodies to the studied strains in the serum. Therefore, native sera cannot be used in diagnostics, but those purified from agglutinins for heterologous groups of Escherichia are needed. When performing serological identification, it should be borne in mind that in strains containing the K-antigen, O-agglutinability appears only after heating, which destroys surface antigens. When working with K(+)-forms (L and B), the bacteria are boiled for an hour.
If the culture retains O-inagglutinability, then it can be assumed that it has an A-antigen. To destroy it, the culture is autoclaved at 1200 for 2 hours. For O-agglutination of K(-) forms, live or killed by heat or formaldehyde bacteria are used.
The term K-antigen combines surface, shell (microcapsules) and true capsular antigens with different properties. Antigen A is a true capsular antigen. It is thermostable; heating at 1000, treatment with formaldehyde and 50% alcohol does not change its properties. Strains with the A-antigen are highly resistant to phagocytosis and bacteriolysis, do not have hemolysins, and are usually less pathogenic. They form intensely turbid colonies, larger in size than the A(-) forms and resembling mucous variants.
L-antigen is destroyed when heated to 1000C for 1 hour. Its presence most often (80%) is the reason for the O-inagglutinability of Escherichia. It protects cells from phagocytosis and bacteriolysis. Strains that have it often have hemolytic and dermatonecrotic properties. Such Escherichia are considered more pathogenic than strains with the A-antigen.
The B antigen occupies an intermediate position in thermolability. It belongs to the envelope or surface somatic antigens. This antigen loses its agglutinability at 1000C (1 hour), and after boiling for 2.5 hours it also loses its antigenic properties, retaining its antibody-binding ability.
K-antigens of each type are serologically heterogeneous. They combine about 100 serologically different surface antigens, which determine the O-inagglutinability of cultures and the features of serological identification of Escherichia: 34 L-antigens, 32 B-antigens, 28 A-antigens. The main criteria for the presence of K-antigens are the O-inagglutinability of living cultures (in a smooth form) and their agglutination in K- or OK-sera.
There is an opinion that the chemical nature of their surface plays a significant role in the pathogenicity of Escherichia. Acidic capsular polysaccharides create a negative charge, which may be important for tissue penetration by Escherichia.
Antigen H has a protein nature. There are 53 known serological varieties of it (numbers 1 to 56). In the same OK- and O-groups of Escherichia there are strains with different H-antigens, which allows them to be differentiated into serovars. Identification of the H-antigen is carried out by immobilization in semi-liquid agar with special sera, or by agglutination method in test tubes or on glass using a 5-7 hour formalinized (0.5%) broth culture, mixing it in equal volumes with serum.
Using commercial preparations produced in our country, it is possible to identify 23 serological varieties of OK groups of Escherichia. The rest (more than 100) remain beyond the diagnostic capabilities of practical laboratories.
consider main biological groups of Escherichia currently allocated. They differ in the presence of special pathogenicity factors and the forms of diseases caused.
A) Escherichia are representatives of normal microflora. This group is very heterogeneous in its properties and is part of the microbiocenoses of various areas of the macroorganism.
B) Escherichia - causative agents of urogenital infections. They most often have the K1 antigen and belong to serogroups 01, 02, 04, 06, 07, 08, 09, 011, 018, etc.
C) Escherichia - pathogens of HVP of different localization (otitis, mastitis, conjunctivitis, abscesses, etc.).
D) Escherichia - pathogens of generalized forms (meningitis, septicemia). Most often they are endogenous strains and cause generalization of the infectious process against the background of a sharp decrease in the immunobiological status of the body and belong to serogroups 01, 02, 04, 06, 025, 075, etc.
D) Escherichia are causative agents of intestinal diarrheal infections. They include several groups.
1. Enteropathogenic Escherichia(EPEC) are causative agents of colienteritis in young children (the first 2 years of life). This group, as a rule, is not dangerous for adults. This includes serogroups: 020, 0111, 0125, 018, 026, 028, 033, 055, 0119, 0142, O18a,c, etc. According to the Nomenclature Committee, when isolated from children up to 1 year of EPEC means that they certainly have an etiological role, and in children aged 1 year to 1 year 11 months 21 days, carriage is possible. In outbreaks caused by EPEC, the source is most often adult carriers, so EPEC is required to screen individuals entering work in children's dairy kitchens. Most EPEC are lactose- and sucrose-positive. Identification is carried out using a serological method to detect O- and K-antigens. It has been shown that the most pathogenic strains are characterized by the presence of certain H-antigens: for O119 - H6, O18 a, c - H7, O142 - H6, etc. There is a relationship between the presence of the H-antigen and a certain biochemical trait, for example, EPEC O111:H2 are sucrose-positive, and O111:H12 are sucrose-negative.
The pathogenesis of diarrhea caused by EPEC is due to its adhesion to the intestinal epithelium and damage to the villi. The bacteria express the eae gene, which causes the release of products that change the architecture of the intestinal mucosa. As a result of massive colonization, an inflammatory reaction develops.
3. Enterotoxigenic Escherichia (ETEC)) - causative agents of cholera-like diseases. Most often these are serogroups 06, 08, 015, 027, 025, 0153, 0159 and others. Biochemically they do not differ from other Escherichia, they are mainly lactose positive. They carry toxigenicity plasmids, which are transmissible and are not firmly linked to a serogroup. Moreover, there are strains that produce a heat-stable toxin (ST) and a labile toxin (LT), close to a choleragen, or simultaneously ST/LT. Many ETEC have such colonization factors - two types of pili: CFA 1 and CFA 2. The synthesis of these factors is determined by a non-transmissible plasmid. According to domestic and foreign authors, more than half of the circulating ETEC strains are characterized by multidrug resistance associated with the presence of plasmids. Among ETEC, strains with colicinogenic and hemolytic properties determined by the Col and Hly plasmids, respectively, are widespread.
These Escherichia can cause 4 types of diseases in all age groups: 1) in underdeveloped countries - gastroenteritis of young children, 2) in developed countries - "travelers' diarrhea", 3) diarrhea of military personnel during combat operations in areas with a hot climate (for example, war in the Persian Gulf), 4) gastroenteritis (similar to food toxic infections) in developed countries (Europe, USA).
The tendency to generalize is not high. In this group there is a nosocomial strain - O1. It is very difficult to differentiate ETEC.
4. Enterohemorrhagic Escherichia (EHEC)- causative agents of hemorrhagic colitis and hematuria. Isolated for the first time in Canada (1982) during an outbreak in a nursing home (mortality rate more than 18%). E. coli 0157:H7 was identified. A toxin close to S.dysenteriae toxin 1 was found in this strain. EHEC also secrete a cytotoxin that causes the death of HeLa and Vero cells in vitro. Subsequently, other serogroups of Escherichia (026) were discovered, causing hemorrhagic colitis and hematuria (multiply in the epithelium of the bladder). Risk groups include children under 1 year of age and persons over 60 years of age. Outbreaks have been reported in Japan, the USA, and Canada. In hemorrhagic colitis, these Escherichia were isolated in 7-34%. The pathogens are characterized by lactose positivity, are not able to break down sorbitol, and are mobile.
5. Enteroadhesive Escherichia (EAEC)) - causative agents of common diarrhea. First isolated in 1985 for diarrhea of unknown etiology, in the absence of Escherichia of the above 4 groups. They got their name due to their ability to adhere to Hep 2 cells in vitro, due to their ability to aggregate on the surface of cell layers. Other pathogenicity factors are not yet known. The group is allocated temporarily.
Escherichia coli
Escherichia coli (Escherichia coli) - gram-negative rod-shaped bacteria, belong to the family Enterobacteriaceae, genus Escherichia (Escherichia), short (length 1-3 µm, width 0.5-0.8 µm), polymorphic motile and immobile, spores do not form. They were first discovered by the German scientist T. Escherich in 1885. E. coli have been isolated from human remains. E. coli is a natural inhabitant of the large intestine of many mammals, particularly primates and humans. The bacteria of the E. coli group include the genera Escherichia (a typical representative of E. coli), Citrobacter (a typical representative of Citr. coli citrovorum), Enterobacter (a typical representative of Ent. aerogenes), which are combined into one family Enterobacteriaceae due to the common morphological and cultural properties.
In the human body, E.coli inhibits the growth of pathogenic bacteria and synthesizes some vitamins. There are varieties of E. coli that can cause acute intestinal diseases in humans. There are more than 150 types of pathogenic (so-called “enterovirulent”) E. coli bacilli, grouped into four classes: enteropathogenic (EPEC), enterotoxigenic (ETEC), enteroinvasive (EIEC) and enterohemorrhagic (EGEC)
Rice. 1 E. coli – electron microscope
Bacteria grow well on simple nutrient media: meat-peptone broth (MPB), meat-peptone agar (MPA). On MPB they produce abundant growth with significant turbidity of the medium; the sediment is small, grayish in color, easily broken. They form a wall ring; there is usually no film on the surface of the broth. On MPA, colonies are transparent with a grayish-blue tint, easily merging with each other. On Endo medium they form flat red colonies of medium size. Red colonies may have a dark metallic sheen (E. coli) or no sheen (E. aerogenes). Lactose-negative variants of Escherichia coli (B.paracoli) are characterized by colorless colonies. They are characterized by wide adaptive variability, as a result of which various variants arise, which complicates their classification.
Rice. 2 Colonies of E. coli on solid nutrient medium
Biochemical properties
Most coliform bacteria (coliforms) do not liquefy gelatin, coagulate milk, break down peptones to form amines, ammonia, hydrogen sulfide, and have high enzymatic activity against lactose, glucose and other sugars, as well as alcohols. They do not have oxidase activity. Based on their ability to break down lactose at a temperature of 37°C, coliforms are divided into lactose-negative and lactose-positive Escherichia coli (LKP), or coliform, which are formed according to international standards. From the LCP group are fecal coliforms (FEC), which are capable of fermenting lactose at a temperature of 44.5°C. These include E. coli, which does not grow on citrate medium.
Stability in the external environment
E. coli is not heat resistant. Bacteria of the coli group are neutralized by conventional pasteurization methods (65 - 75 ° C). At 60°C, E. coli dies within 15 minutes. A 1% solution of phenol causes the death of the microbe in 5-15 minutes, sublimate in a dilution of 1:1000 - in 2 minutes, is resistant to the action of many aniline dyes. The persistence of E. coli at low temperatures and in various environmental substrates has not been sufficiently studied. According to some data, E. coli can persist in water and soil for several months.
Sanitary indicative value The sanitary indicative value of individual genera of coliform bacteria varies. The detection of bacteria of the genus Escherichia in food products, water, soil, and equipment indicates fresh fecal contamination, which is of great sanitary and epidemiological significance. It is believed that bacteria of the genera Citrobacter and Enterobacter are indicators of older (several weeks) fecal contamination and therefore they have less sanitary indicative value compared to bacteria of the genus Escherichia. With long-term use of antibiotics, various variants of Escherichia coli are also found in the human intestine. Of particular interest are lactose-negative variants of Escherichia coli. These are modified Escherichia that have lost the ability to ferment lactose. They are released during human intestinal infections (typhoid fever, dysentery, etc.) during the recovery period. The greatest sanitary indicators are E. coli that do not grow on Coser’s medium (citrate medium) and ferment carbohydrates at 43-45 ° C (E. coli). They are an indicator of fresh fecal contamination.
Diseases caused in humans by E.coli
Intestinal diseases caused by pathogenic E.coli are collectively called escherichiosis. The terms coli infection, coli enteritis, traveler's diarrhea, and colibacillosis are also used.
Escherichiosis refers to acute intestinal diseases (AID) with a fecal-oral mechanism of infection. Each of the above classes of pathogenic E. coli is characterized by certain differences in the course of the disease, which in its symptoms may resemble cholera or dysentery. The incubation period lasts 3-6 days (usually 4-5 days).