Yersinia

Y. Pseudotuberculosis and Y. Enterocolitica do not belong to the category of especially dangerous, but they also play a significant role in human pathology. Y. Pseudotuberculosis and Y. Enterocolitica are polymorphic, non-controversial gram-negative rods, which are often ovoid in form, cells in old cultures are unevenly colored. Bacteria of pseudotuberculosis, taken from wet agar, can have a bipolar color, form a capsule, but with varying degrees of severity. Both types of bacteria have, in contrast to Y. Pestis, mobility due to the presence of peritricchial flagella. Mobility is detected by sowing in a column of semiliquid agar with a prick, but only at 18-20 ° C, at 37 ° C it is absent. Yersinia are undemanding to nutrient media, grow well on common universal media, are able to actively multiply in soil and water. The optimum temperature for growth is 30 ° C, the upper and lower temperature growth limits are 43 ° C and 0-2 ° C, respectively, and the pH range is 6.6-7.8. On Wednesday, the colonies have a diameter of 0.1-0.2 mm, round, convex, shiny, with even edges, colorless (do not ferment lactose), after a few days the size of the colonies is 0.5-3 mm. The colonies of the causative agent of pseudotuberculosis, which are in R-form, almost do not differ from the colonies of Y. Pestis (pigmented center and scalloped "lace" edge), but do not have the stage of "broken glass".

All three types of Yersinia differ in antigenic properties.

The causative agent of pseudotuberculosis according to O-antigens is divided into eight groups (I-VIII) with 20 O-factor antigens (1-20). According to O- and H-antigens (a-e), this species is divided into 13 serovars and sub-serovars (la, lb? IIa, IIb, IIc, III, IVa, IVb, Va, Vb, VI, VII, VIII).

Y. Enterocolitica is characterized by heterogeneity in the O-antigen. There are 34 serovars of this species. Most of them are adapted to some types of animals or are widely distributed in the external environment. The overwhelming majority of strains isolated from humans belong to the serovars 03 and 09, less common are serovars 06, 08, 05 and very rarely serovars 01, 02, 010, 011, 013-017.

From patients with pseudotuberculosis, strains of serovars I (lb), III and IV are most often isolated.

During the evolution of Yersinia, the necessity of existence in two habitats - the external (saprophytic phase) and in the body of warm-blooded animals and man (the parasitic phase) was fixed. To implement the parasitic phase, iersinia must penetrate into the body of the warm-blooded animal. Infection with the causative agent of pseudotuberculosis most often occurs when food is eaten by iersinia infected foods stored at a low temperature (4-12 ° C) in refrigerators and vegetable stores. In these conditions, due to their psychrophilicity, bacteria can multiply and accumulate in food substrates. An example of such a method of infection is a disease in 1988, pseudotuberculosis 106 people in the Krasnodar region, associated with the use of cabbage infected with Y. Pseudotuberculosis. Its main reservoir is the soil.

Yersinia at a low temperature have a high potential of cellular and tissue invasiveness and are able to maintain a high level of virulence, but the pathogen can penetrate the human body and through any mucous membranes, probably due to nonspecific mechanisms. The source of iersiniosis is also wild and synanthropic rodents, domestic and farm animals. It is possible to infect a person from a person.

Y. Pseudotuberculosis strains are isolated from 175 mammalian species, 124 bird species, and 7 fish species. Infected rodents, animals and humans excrete the pathogen with feces and urine, contaminating water, plants and other objects of the environment, and through them a person becomes infected. Thus, the food pathway in the transmission of pathogens of pseudotuberculosis and intestinal yersiniosis is leading: infection occurs as a result of eating raw or insufficiently thermally processed foods (meat, meat products, milk, vegetables, fruits, greens). Both types of pathogens are able to multiply not only on plants, but also inside them (salad, peas, oats, etc.).

Diseases caused by Yersinia are characterized by the polymorphism of clinical manifestations, gastrointestinal tract damage, the tendency to generalization, septicopyemia and the defeat of various organs and systems.

Y. Enterocolitica causes a person gastroenteritis with damage to the walls of the small intestine. Often after the disease, autoimmune spondyloarthritis such as Reiter's syndrome and reactive arthritis are observed. It is believed that these effects are associated with the presence of Y. Enterocolitica superantigens. The properties of superantigens are possessed by membrane proteins of these bacteria.

Pseudotuberculosis of people in the Far East is described as Far Eastern scarlet fever. It is more severe than pseudotuberculosis in the western regions, and is characterized by more severe allergic and toxic manifestations, especially at the 2 nd stage of the disease.

The pathogenic properties of Yersinia of both species, as well as the causative agent of plague, are determined not only by chromosomal, but also plasmid genes. They found plasmids very similar to the plasmids of U. Pestis, which code for the synthesis of VW antigens and outer proteins (Yop), the same as those of U. Pestis, and other virulence factors. They have a common cluster of W. Pestis cluster genes associated with the iron transport system. It is established that Y. Pseudotuberculosis synthesizes a thermostable toxin that causes the death of guinea pigs during intraperitoneal infection. An ability of the pathogen to adhere and colonize the intestinal mucosa plays an important role in the pathogenesis of pseudotuberculosis.

Microbiological diagnosis of yersiniosis includes the use of bacteriological methods and serological reactions. In the bacteriological method, the test material from the patient (stool, blood, mucus from the pharynx), as well as suspicious products or water, are inoculated on Endomo, Ploskireva, Serova (indicator and differential) media and incubated at 37 ° C for 48-72 hours. Suspicious colonies (small colorless on mediums Endo and Ploskireva and stained colonies of two different forms on Serov media) are transected to obtain pure cultures that are identified by biochemical characteristics and finally typed using diagnostic agglutinating serums.

For serological diagnosis of pseudotuberculosis and intestinal yersiniosis, a detailed agglutination reaction (according to the type of Vidal's reaction) is used with appropriate diagnosticums or RPHA with an antigenic erythrocyte diagnosticum. Positive reactions are considered at an antibody titer of 1: 400 and above. It is recommended that the reaction be performed with paired sera at intervals of several days. Increasing the antibody titer indicates the specificity of the infectious process.