What is Salmonellosis?
Salmonellosis is an acute zoonotic intestinal infection characterized by lesions of the digestive organs with the development of intoxication syndrome and water-electrolyte disorders, less often with typhoid-like or septicopyemic course.
Brief historical information
The first representatives of the genus were found by K. Ebert (1880) in Peyer’s patches, spleen, and lymph nodes of a person who died of typhoid fever; G. Gaffky singled out a pure culture of the causative agent of the disease (1884). Later D.E. Selmon and J. T. Smith (1885) during the outbreak of swine fever and A. Gertner (1888) isolated similar bacteria from the beef and spleen of the deceased person. At the beginning of the 20th century, a separate genus was organized for pathogens in the Enterobacteriaceae family, which was named Salmonella in honor of Salmon. Salmonella are a large group of bacteria, the systematics of which underwent significant changes with the improvement of knowledge about their antigenic structure and biochemical properties. In the early 1930s, F. Kauffmann and P. White proposed to divide salmonella in accordance with their antigenic structure; it is currently used to differentiate Salmonella.
Causes of Salmonellosis
The causative agents are Gram-negative motile sticks of the Salmonella genus of the family Enterobacteriaceae, which unites more than 2,300 serovars, divided by a set of somatic O-antigens into 46 serogroups. According to the structure of the H-antigen, about 2500 serovars are isolated. Despite the abundance of detectable serum variants of Salmonella, the majority of salmonellosis diseases and carrier cases in humans are due to a relatively small number of serovars (10-12). The last classification of Salmonella (1992) identifies two types: S. enterica and S. bongori, which in turn are subdivided into 7 subspecies (subgenera), denoted by numbers or proper names – S. enterica (I), salamae (II), arizonae (III ), diarizonae (IIIb), houtenae (IV), indica (V) and bongori (VI). The main pathogens of salmonellosis are part of the I and II subgenera. The division into subspecies has a certain epidemiological significance, since the natural reservoir of Salmonella I subspecies is warm-blooded animals, and for the other subspecies it is cold-blooded animals and the environment. Bacteria grow on common nutrient media, have a complex antigenic structure: they contain a somatic thermostable O-antigen and a flagellate thermolabile H-antigen. Many representatives identify surface Vi-antigen. Some serotypes are phagotyped. Most salmonella are pathogenic both for humans and for animals and birds, but in epidemiological terms only a few of them are most significant for humans. S. typhimurium, S. enteritidis, S. panama, S. infantis, S. newport, S. agona, S. derby, S. london and some others cause 85-91% of cases of salmonellosis. At the same time, the share of the first two accounts for 75% of all isolates currently isolated from sick people.
Salmonella is long preserved in the environment: in water up to – 5 months, in meat – about 6 months (in bird carcasses more than a year), in milk – up to 20 days, kefir – up to 1 month, in butter – up to 4 months, cheeses – up to 1 year, in egg powder – from 3 to 9 months, on eggshell – from 17 to 24 days, in beer – up to 2 months, in soil – up to 18 months. It was established experimentally that during long-term (over a month) storage of eggs in the refrigerator S. enterica can penetrate into the eggs through the intact shell and multiply in the yolk. At 70 ° C they die for 5-10 minutes, in the thicker piece of meat they withstand boiling for some time, during the process of cooking eggs they remain viable in protein and yolk for 4 minutes. In some products (milk, meat products), salmonella can not only be preserved, but also reproduce, without changing the appearance and taste of products. Salting and smoking have a very weak effect on them, and freezing even increases the time it takes for microorganisms to survive in food. Known so-called resident (hospital) strains of Salmonella, characterized by multiple resistance to antibiotics and disinfectants.