What causes salmonellosis?

Causes of Salmonella

According to the structure of the O-antigen, salmonella is divided into groups A, B, C, D, E, etc., and by flagellate H-antigen - into serovars. There are about 2000 serovars. More than 700 serovars have been allocated from man. In our country more than 500 are recorded. Salmonella of groups B, C, D predominate among them. E - Salmonella enteritidis, S. Typhimurium, S. Derby, S. Panama, S. Anatum, S. Choleraesuis.

Pathogenesis of salmonella

The development of the infectious process largely depends on the mechanism of infection (food, contact, etc.). The magnitude of the infecting dose and the degree of pathogenicity of the pathogen, the immune defense of the macroorganism, age, etc. In some cases, intestinal infection proceeds violently, with the development of endotoxin shock. Expressed toxicosis with exsicosis or generalized infectious process (septic forms) and with significant bacteremia (typhoid-like forms), and in others - there are erased, subclinical forms or bacteriocarrier. Regardless of the form of the disease, the main pathological process develops in the digestive tract and mainly in the small intestine.

• Live bacteria are destroyed in the upper gastrointestinal tract (in the stomach, small intestine), resulting in the release of a large number of endotoxins. Which, absorbed into the blood, cause a toxic syndrome ("toxemia phase"), which determines the clinical picture of the initial period of the disease.
• If bacteriolysis is not enough, and factors of nonspecific protection of the digestive tract are imperfect (children of early age, newborns, weakened, etc.), salmonella enter the small intestine unhindered, and then into the thick one, where the primary localization of the pathological process takes place ("enteral phase").

Possessing pronounced invasiveness and cytotoxicity for the intestinal epithelium and, to a greater extent, for the underlying tissue, salmonella are not only capable of initial colonization of the epithelium surface, but also can penetrate (within the phagosome-like vacuoles) into the epitheliocytes, into the own plate of the mucosa, into macrophages and multiply in them. Colonization of the epithelium of both the small and large intestine, the reproduction of Salmonella in epithelial cells (and macrophages) lead to thinning, fragmentation and rejection of microvilli, destruction of enterocytes and development of pronounced catarrhal and granulomatous inflammation, which serves as the main pathogenetic mechanism for the development of diarrheal syndrome (enteritis or enterocolitis) .

• Depending on the state of the immune system of the body and, in the first place, the cellular immunity, other factors of nonspecific defense, either a local inflammatory process occurs or a breakthrough of the intestinal and lymphatic barriers occurs and the next stage of the infectious process ("bacteremia phase") occurs . With the blood flow, salmonella enter various organs and tissues, where they can also multiply ("secondary localization") with the development of lymphohistiocytic and epithelioid granulomas in cells and the formation of septic foci (meningitis, endocarditis, osteomyelitis, peritonitis, etc.) (septic form).

Due to severe diarrheal syndrome, repeated vomiting and other factors, toxicosis syndrome with exsicosis develops. As well as hemodynamic disorders. Functions of the cardiovascular, central and autonomic nervous system, metabolism, with the inhibition of kidney function, the liver and often the adrenal cortex. The development of toxicosis with exsicosis heavens the main infectious process and can often be the cause of an unfavorable outcome.

Intracellular parasitization of Salmonella in the intestinal epitheliocytes (including macrophages) determines the possibility of their persistent persistence in the body, the emergence of exacerbations and relapses, as well as the formation of prolonged bacterial release and low effectiveness of antibiotic therapy.