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What causes escherichiosis?
Last reviewed: 19.11.2021
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Escherichiosis is caused by Escherichia - mobile gram-negative rods, aerobes, related to the species Escherichia coli, the genus Escherichia, the family Enterobacteriaceae. They grow on ordinary nutrient media, they release bactericidal substances-colicins. Morphologically the serotypes do not differ from each other. Escherichia contain somatic (O-Ar-173 serotype), capsular (K-Ar-80 serotypes) and flagellate (H-Ar-56 serotypes) antigens. Diarrhea E. Coli are divided into five types:
- enterotoxigenic (ETCP, ETEC);
- enteropathogenic (EPPC, EPEC);
- Enteroinvazivnye (EIKP, EIEC):
- enterohemorrhagic (EHEC, EHEC);
- Entero-adhesive (EACC, EAEC).
Pathogenicity factors ETKP (saws, or fimbrial factors) determine the tendency to adhesion and colonization of the lower parts of the small intestine, as well as to toxin formation. Thermolabile and thermostable enterotoxins are responsible for increased fluid excretion into the lumen of the gut. The pathogenicity of EPOC is due to its ability to adhere. EIKP are capable, having plasmids, to penetrate into the cells of the intestinal epithelium and multiply in them. EHEC release cytotoxin, shigopodobnye toxins of the 1 st and 2 nd types, contain plasmids, which facilitate adhesion to enterocytes. Pathogenicity factors of entero-enteric coli have not been studied enough.
Escherichia are stable in the environment, can last for months in water, soil, excrement. They remain viable in milk up to 34 days. In children's nutritious mixtures - up to 92 days, on toys - up to 3-5 months. Dry drying is well tolerated. Possess the ability to reproduce in food, especially in milk. Quickly die when exposed to disinfectants and boiling. Many strains of E. Coli have multidrug resistance to antibiotics.
Pathogenesis of Escherichiosis
Escherichia penetrate through the mouth, bypassing the gastric barrier, and depending on the type of accessory is pathogenic.
Enterotoxigenic strains are capable of producing enterotoxins and a colonization factor, through which attachment to enterocytes and colonization of the small intestine are carried out.
Enterotoxins are thermolabile or heat-stable proteins that act on the biochemical functions of the crypt epithelium without causing visible morphological changes. Enterotoxins increase the activity of adenylate cyclase and guanylate cyclase. With their participation and as a result of the stimulating effect of prostaglandins, the formation of cAMP increases, as a result of which a large amount of water and electrolytes are secreted into the lumen of the intestine, which do not have time to be reabsorbed in the large intestine; watery diarrhea develops, followed by disturbances in the water-electrolyte balance. The infecting dose of ETCP is 10x10 10 microbial cells.
EHEC have the property of being introduced into the colon epithelium of the colon. Penetrating into the mucous membrane, they cause the development of an inflammatory reaction and the formation of erosions of the intestinal wall. Due to damage to the epithelium, the absorption of endotoxins into the blood increases. At patients in excrements appear slime, a blood and polymorphic-nuclear leucocytes. Infectious dose of EIKP - 5x10 5 microbial cells.
The mechanism of EPOC pathogenicity has not been studied sufficiently. The strains (055, 086,0111, etc.) revealed the adhesion factor to the Hep-2 cells, due to which colonization of the small intestine occurs. In other strains (018, 044, 0112, etc.) this factor was not detected. The infecting dose of EPPC is 10x10 10 microbial cells.
EHEC release a cytotoxin (SLT-shiga-like toxin) that destroys endothelial cells lining the small blood vessels of the intestinal wall of the proximal colon. Blood clots and fibrin interfere with the blood supply of the intestine - blood stains in the stool. Developed ischemia of the intestinal wall, down to necrosis. Some patients experience complications with the development of the syndrome of disseminated intravascular coagulation (ICD), ITH and acute renal failure.
EACP are capable of colonizing the small intestine epithelium. The diseases of adults and children caused by them proceed for a long time, but easily. This is due to the fact that the bacteria are firmly fixed on the surface of epithelial cells.