Microbiology: lecture notes Ksenia Viktorovna Tkachenko

3. Shigella

3. Shigella

They belong to the genus Shigella.

They are causative agents of dysentery. The morphology is the same as that of other representatives of the Enterobacteriaceae family. They are immobile and do not form capsules.

They grow well on simple nutrient media. Colorless colonies form on Endo medium.

The genus includes four species that differ in biochemical properties (the ability to ferment mannitol and lactose) and antigenic structure:

1) Sh. disenteriae; do not ferment lactose and mannitol; according to antigenic properties within the species they are divided into 12 serovars; one of them, Shigella Grigorieva-Shiga, is the most pathogenic;

2) Sh. flexneri; ferments only mannitol; according to antigenic properties it is divided into 6 serovars, which are divided into subserovars;

3) Sh. boydii; ferments only mannitol; according to antigenic structure it is divided into 18 serovars;

4) Sh. sonnei; ferments only lactose; Antigenically, the species is homogeneous; within the species, fermentovars, phagovars, and kolecinovars are distinguished.

Shigella, bypassing the stomach and small intestine, enters the large intestine. They attach to colonocyte membrane receptors and penetrate inside using the outer membrane protein. Cell death leads to the formation of erosions and ulcers surrounded by perifocal inflammation.

Pathogenicity factors:

1) proteins of the outer membrane (provide the ability for invasion and intracellular reproduction);

2) contact hemolysin (promotes lysis of cell vacuole membranes);

3) exotoxin (has enterotropic, cyto- and neurotoxic effects);

4) endotoxin (has a general toxic effect on the body and protects Shigella that has entered the body from the action of the protective forces of the macroorganism).

There are three clinical forms of dysentery, which differ in pathogens, epidemiology and partly in clinic:

1) Grigoriev-Shiga dysentery. Pathogen – Sh. disenteriae, serovar – Shigella Grigorieva-Shiga. Routes of transmission: nutritional, contact and household. Features of the clinic: it is severe, characterized by bloody diarrhea with blood, symptoms of central nervous system damage, there may be bacteremia;

2) Flexner's dysentery. Pathogens – Sh. flexneri and Sh. boydii. The route of transmission is water. Features of the clinic: it occurs as typical dysentery of varying severity;

3) Sonnei dysentery. The route of transmission is food. Features of the clinic: there may be symptoms of food poisoning, vomiting.

Diagnostics:

1) bacteriological examination;

2) immunoindication (ELISA);

3) serodiagnosis (has retrospective significance).

Specific prevention: dysentery bacteriophage (used in areas of infection).

Etiotropic therapy: in moderate and severe cases of the disease, antibiotics are prescribed (those that are excreted by the intestines) taking into account the sensitivity of the pathogen.

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 (lat. shigella) is part of the family of enterobacteria (lat. enterobacteriaceae), the order of enterobacteria (lat. enterobacteriales), the class of gamma-proteobacteria (lat. γ proteobacteria), the type of proteobacteria (lat. 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 factors environment. Shigella lives in water, soil, food products, 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 predominant damage to the distal 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 contact-household route, through water and food. 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, lethal shigellosis, unlike a number of other foodborne infections, has not been reported.

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, and 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 supply of the population food products. 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 capsule 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 are 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 EPEC clearly means their 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 - pili of two types: 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 are capable of causing 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, the Gulf War), 4) gastroenteritis (according to type of foodborne diseases) 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 microns, width - 0.5-0.8 microns), polymorphic motile and non-motile, 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 bacteria of the coli group (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 coliforms, which are formed by 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 in the human intestine, various options coli. 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).

Causative agents of bacterial dysentery is a group of bacteria grouped under the genus Schigella.

The etiological role of these microbes in dysentery was first established by the Russian scientist A.V. Grigoriev (1891) and the Japanese researcher Shiga (1898). Subsequently, other types of bacteria that cause dysentery were isolated and described: Kruse - in 1900, Flexner and Strong - in 1900, Sonne - in 1915, Schmitz and Stutzer - in 1917, Boyd - in 1932-1942 gg., E.M. Novgorod - in 1943, etc.

Morphology and biological properties. Like all members of the family of intestinal bacteria, the causative agents of dysentery are small rods measuring 2-3 microns. They are gram-negative and do not form spores or capsules. They do not have flagella, which is one of the characteristics that allows them to be distinguished from motile Salmonella. All of them are facultative anaerobes and grow well on simple nutrient media at a temperature of 37°C and pH 7.2-7.4. Colonies on solid media are translucent, delicate, and their growth patterns do not differ from Salmonella colonies. Biochemical properties individual species The causative agents of dysentery are different. They ferment carbohydrates with the formation of acid without gas (with the exception of Shigella Newcastle); they break down glucose and do not ferment lactose (except for Shigella Sonne). In relation to mannitol, all Shigella are divided into two groups: mannitol-positive and mannitol-negative. Shigella reduces nitrates into nitrites, does not liquefy gelatin, and does not break down urea.

Toxin formation. A strong exotoxin of a protein nature was found only in Shigella dysentery Grigoriev-Shiga. Intravenous administration of it to white mice and rabbits causes paralysis of their hind limbs. The remaining causative agents of dysentery contain a heat-stable endotoxin, which is a lipopolysaccharide-protein complex. It has enterotropic and neurotropic properties.

Sustainability. The causative agents of bacterial dysentery persist for 5-10 days in water, soil, and on various products and objects. At low temperatures they remain viable for up to 2 months. A temperature of 60°C kills them within 10-20 minutes. Under the influence of 1% carbolic acid, chloramine, bleach, Shigella die in 30 minutes. They quickly become resistant to antibiotics and sulfa drugs.

Antigenic structure. Shigella has somatic O- and surface K-antigen. The presence of antigens common to other representatives of the family of intestinal bacteria has been established. Shigella dysentery Grigoriev-Shig, Shtutser-Schmitz and Shigella Sonne contain only isolated species antigens. Shigella dysentery Large-Sachs and Shigella Boyd include different typical antigens. The antigenic structure of Shigella Flexner is the most complex. They have various type-specific and group antigens that determine belonging to one or another type and subtype.

Classification. According to the classification adopted in the Soviet Union (1962), all Shigella are divided into three groups (Table 5).

The first group includes species of Shigella dysentery that do not break down mannitol: Grigoriev - Shig, Shtutser - Schmitz, Large - Sachs and provisional.

The second group is mannitol-splitting agents, which include the Shigella Flexner species: Shigella Flexner itself (5 types) with the subspecies Newcastle and Boyd. The latter are divided into 15 types, differing in antigenic composition.

The third group ferments mannitol and slowly ferments lactose (within 48 hours) - Shigella Sonne. On solid media, Shigella Sonne forms S- and R-form colonies.

There are three fermentative types of these bacteria, which ferment rhamnose and xylose differently.

In accordance with the International Classification, the genus Schigella is divided into 4 groups, which differ from each other in enzymatic activity and antigenic structure.

1. Group A (Sh. dysenteriae): Shigella dysentery of Shig, Schmitz and Large-Sachs, among which 5 serological types are distinguished.

2. Group B (Sh. flexneri): Shigella Flexner of 6 types, differing in the composition of antigens, including Shigella Newcastle.

3. Group C (Sh. boydii): 15 serological types.

4. Group D (Sh. sonnei).

Pathogenicity. Dysentery only affects humans. Among animals, the clinical picture of dysentery can only be reproduced in monkeys. After microbes are administered intravenously to white mice and rabbits, they die within a few days. At autopsy, selective damage to the small and large intestines is revealed. Dysenteric microbes are able to multiply in the cells of the cornea of ​​a guinea pig's eye, causing characteristic keratoconjunctivitis. IN recent years a connection has been established between the strain’s ability to cause keratoconjunctivitis when injected into the conjunctiva of a guinea pig’s eye and its virulence. Virulent strains lead to the development of keratoconjunctivitis within 24-48 hours. M.K. Voino-Yasenetskaya developed in 1957 a model of intranasal infection of white mice with freshly isolated cultures of dysentery microbes. It turned out that they quickly (within 24 hours) multiply in the epithelium of lung tissue. An autopsy reveals a picture of multiple focal pneumonia.

Pathogenesis and clinic. The source of infection is a person - a patient or a bacteria carrier, with whose feces the microbes enter the external environment. Having entered the intestines with food, dysentery microbes penetrate the mucous membrane of the large intestine and multiply there: some of them die. Endotoxin, released when the pathogen is destroyed, is absorbed into the blood, causing general intoxication of the body, sensitizing the intestinal mucosa, and increasing the permeability of its blood vessels. Local changes in the large intestine (catarrhal-diphtheritic inflammation, necrosis, ulcers) are the result of exposure to endotoxin and other toxic substances formed in the intestine under the influence of bacteria.

Incubation period lasts from 2 to 7 days. Then the temperature rises, cardiovascular and nervous systems, vomiting, frequent loose stools mixed with mucus and blood, tenesmus. If the outcome is favorable, after 8-10 days the stool returns to normal, the symptoms of intoxication disappear, and recovery occurs. There are cases of longer lasting dysentery; a transition to a chronic form is possible, which is characterized by periodic relapses of the disease.

Immunity. A person has a fairly pronounced natural immunity to dysentery infection, so infection does not always lead to illness. After an illness, a low-strength and relatively short-lived species-specific immunity remains. It is more pronounced in Flexner's dysentery and short-lived in Sonne's dysentery. Antimicrobial immunity (for dysentery caused by Shigella dysentery Grigoriev - Shiga, antitoxic). Great value has local cellular-tissue immunity associated with the emergence of resistance of the intestinal epithelium to invasion of dysentery bacteria.

Microbiological diagnostics. The main method is microbiological examination of the patient's stool.

Sowing must be done as quickly as possible after taking the material. If this option is not available, feces are placed in a test tube with a preservative (glycerol or phosphate buffer mixture), where they can be stored for up to 12-24 hours (at a temperature of 4°C). The material can be collected using a glass rectal tube that is inserted into the rectum.

On the 1st day, feces containing mucopurulent lumps are inoculated into a test tube with a selenite enrichment medium, which promotes the accumulation of dysentery microbes and inhibits the growth of E. coli and other saprophytes. At the same time, inoculate two plates with dense media: Levin or Endo and Ploskireva. Due to the fact that in recent years many antibiotic-resistant and antibiotic-dependent strains of Shigella have appeared, the material is inoculated on the same media, adding chloramphenicol. The crops are incubated in a thermostat at 37°C for 24 hours.

On the 2nd day, the grown colonies are examined and suspicious ones (colorless on differential diagnostic media) are screened out onto a short “variegated row” or Ressel’s medium. From the enrichment medium, they are subcultured onto differential diagnostic media (Endo, Levin, Ploskireva). The further course of the study is similar to the primary crops on these media.

On the 3rd day, changes are noted on Ressel's medium. The culture, which does not decompose lactose and ferment glucose with the formation of acid, is subjected to further study: microscopically, to study the biochemical properties, inoculation is done on an expanded “variegated row”, for the purpose of serological identification, an agglutination reaction is performed - first tentatively, with polyvalent agglutinating dysentery sera, then with species or typical and group.

On the 4th day, the microbiological study is completed: changes in the “variegated row” (carbohydrate fermentation), the result of the agglutination reaction, are taken into account.

An auxiliary method of laboratory diagnostics is a serological test - an agglutination reaction with the patient's serum and various diagnostics of dysentery microbes. In recent years, erythrocyte diagnostics from Shigella Sonne and Flexner have become widespread, with the help of which the presence of antibodies is determined in patients and those who have recovered from the disease using a passive or indirect hemagglutination reaction (IPHA).

Isolation of dysentery phage using the reaction of increasing phage titer and scatological examination are used as additional methods of laboratory diagnosis.

As an additional diagnostic method for suspected dysentery, an intradermal allergy test with dysenterine, which is a protein fraction of the dysenteric Shigella Flexner and Sonne, is also used.

The skin allergy test is positive in 75-80% of patients, but in 20-25% of cases it can be positive in persons with non-dysenteric diseases. Specific sensitization develops from the 3rd-4th day of the disease and begins to fade by the end of the 3rd week.

Prevention and treatment. The main preventive measures are the early identification of patients and bacteria carriers, their full treatment and sanitation, and the implementation of sanitary and anti-epidemic measures in the source of infection.

Specific prophylaxis is currently almost never used, since the previously used killed and chemical vaccines, as well as the Bezredki enteral vaccine, turned out to be ineffective. Vaccines have been obtained from live mutants of avirulent strains of dysentery microbes. In foci of infection, a polyvalent dysentery bacteriophage is used, which is given to persons who have been in contact with patients with dysentery.

Treatment is carried out comprehensively: a combination of sulfonamide drugs (phthalazole, sulgin, sulfadimezin, norsulfazole) with antibiotics (chloramphenicol, tetracycline, ampicillin) and restorative therapy are required. From the first days of the disease, dysentery bacteriophage is used. For the treatment of chronic dysentery, dry alcohol dysentery vaccine, a vaccine from killed ethyl alcohol dysentery microbes Flexner and Sonne.

Epidemiology. The source of infection is only a person suffering from acute or chronic dysentery, or who is a carrier of the bacteria. The mechanism of transmission is fecal-oral, routes: 1) nutritional (the predominant route for Shigella Zone); 2) aquatic (predominant for Shigella Flexner); 3) contact-household (is leading for Sh. dysenteriae).

A feature of the epidemiology of dysentery is the change in the species composition of pathogens. Until the end of the 30s of the twentieth century, the share of Sh. Dysenteriae accounted for up to 30–40% of all cases of dysentery, then this serovar became less common and almost disappeared. However, in the 60s - 80s Sh. dysenteriae1 serovar reappeared and caused a series of epidemics that led to the formation of three hyperendemic foci - in Central America, Central Africa and South Asia.

The reasons for the change in the species composition of dysentery pathogens are apparently associated with changes in collective immunity and changes in the properties of dysentery bacteria. In particular, the return of Sh. dysenteriaeI serovar and its widespread distribution are associated with its acquisition of plasmids that lead to multidrug resistance and increased virulence.

Currently, diseases caused by Sh. Sonnei And Sh. flexneri. People's natural susceptibility to dysentery is high. Dysentery is widespread. Diseases usually occur in the form of outbreaks of a nutritional or waterborne nature. Children under 10 years of age are most often affected. Summer-autumn seasonality is typical. Shigella affects the distal parts of the large intestine - the sigmoid and rectum, causing dysentery. Dysenteria is an acute infectious disease that is clinically manifested by frequent painful stools with bloody-mucous stools and intoxication.

Pathogenesis. Shigella attaches to M cells that cover the regional lymphatic formations of the intestinal submucosa. Shigella penetrates the submucosa through M cells, where they are absorbed by macrophages. The interaction of Shigella with macrophages leads to the death of the latter, resulting in the release of IL-1 and IL-18, which cause acute inflammation in the submucosa with the involvement of a large number of neutrophils. The death of phagocytes allows Shigella to remain viable and penetrate into epithelial cells mucous membrane through the basement membrane. Shigella multiplies inside enterocytes and penetrates neighboring cells, which leads to the appearance of erosions. As a result of the death of Shigella, Shiga toxin, Shiga-like toxins and endotoxin are released, which leads to the appearance of blood in the stool. The incubation period of dysentery ranges from several hours to three to five days. The phenomena of acute colitis develop gradually or immediately. Characterized by sharp, colicky abdominal pain and frequent, false, painful urge to defecate - tenesmus (up to 20 - 30 times a day). The stool becomes mucous-watery, mixed with mucus and pus, and with more severe dysentery - blood, pus and particles of the intestinal mucosa. The disease lasts 1 – 3 weeks. Atypical, erased forms may occur. Diseases caused by Sh. sonnei, can begin as foodborne toxic infections. In approximately 3% of cases, the disease becomes chronic, and in 2% a long-term carrier state of the bacteria develops.

According to the morphological characteristics of Shigella indistinguishable from other members of the family Enterobacteriaceae. Dysentery bacteria They do not have capsules; on solid media they form smooth (S-) and rough (R-) colonies. S-colonies are round, dome-shaped, smooth, translucent in transmitted light.

R-colony dysentery irregular shape, flat, dull, with a rough surface and uneven edges. In liquid media S-form of dysentery give uniform turbidity, R-forms form bottom sediment, the medium remains transparent.

Biochemical properties of dysentery

Compared to other intestinal bacteria, biochemically shigella inert (see Table 18-1). All Shigella do not produce H 2 S and do not ferment lactose on Kligler agar. Indole production is variable (it is produced by more than half of the strains of S. dysenteriae, S. flexneri and S. boydii). In some cases, determining the properties of bacteria using a minimum differentiating series can also give an approximate idea of ​​the species.

Has the least enzymatic activity S. dysenteriae ( Grigoriev-Shiga-Kruse wand). Bacteria ferment only glucose without producing gas. Because they do not degrade mannitol, while other species ferment it, they are also known as mannitol-negative Shigella.

S. flexneri ( Flexner stick) does not ferment lactose, dulcite and xylose; almost all rods form indole. Bacteria of serological group 6 (also known as Shigella Manchester and Newcastle) produce small amounts of gas when fermenting glucose and other fermentable carbohydrates.

Very similar biochemical activity S. boydii also possess them, but they also ferment xylose, dulcite and arabinose (usually in the first 24 hours). Some Shigella Bonda are also capable of fermenting maltose (on days 6-20), which is of practical importance in identifying cultures.

S. sonnei does not ferment sorbitol and dulcite do not form indole, but break down xylose and arabinose, which makes them similar to Shigella Bonda. Distinctive feature- the ability to grow at 45 C, ferment rhamnose, as well as lactose and sucrose at a later date.