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Relevance. This study is related to the study of the etiology, pathogenesis and clinic of inflammatory bowel diseases (IBD). In a number of patients with IBD who are refractory to anti-inflammatory/immunosuppressive therapy, there are signs of current or transferred yersiniosis infection, not diagnosed by routine methods.Aim. According to the scientific literature and the results of our own research, to identify the presence and assess the nature of the influence of yersinia on the occurrence and development of IBD.Materials Methods. In our study, we conducted a bacteriological examination of feces by polymerase chain reaction (PCR) in patients with a diagnosis of IBD (UC and CD) in the acute phase (MMDAI ≥ 4 points for UC and Best index ≥ 150 points for CD), as well as immunological diagnostics using enzyme immunoassay (IFA) in the version of line-blotting (IB). Using the results obtained, clinical and instrumental semiotics were evaluated in subgroups of individuals suffering from IBD with confirmed yersiniosis ("IBD+ IER+") and without it ("IBC+ IER–"). We also assessed the role of intestinal infection by determining the effectiveness of initial antibacterial therapy in the treatment of exacerbation of IBD.Results. A significant part (in the case of our sample – 45%) of patients with IBD, when examined by high-tech methods, demonstrate the presence of markers of a transferred or current yersiniosis infection. Its role in the initiation and development of autoimmune intestinal inflammatory process requires further clarification.Conclusions. In 45% of patients with IBD, high-precision examination reveals markers of transferred or current yersiniosis infection. Routine clinical methods for the diagnosis of yersiniosis have low sensitivity and do not allow us to convincingly assess the role of this bacterial agent as a trigger factor for the onset or recurrence of IBD. There is a tendency for greater manifestation in the debut of IBD in patients with markers of systemic yersiniosis. The fact of improvement against the background of empirical antibacterial therapy in 24% of patients with IBD, achievement of early clinical remission in 57% of patients receiving antibiotic therapy, indicates a significant role of bacterial enterocolopathogens in the genesis of chronic intestinal inflammation in a number of patients.

The first case of COVID-19 was registered in the Leningrad Region on March 13, 2020. The period of increasing intensity of the epidemic process lasted 8 weeks. One month after reaching the maximum incidence rate, a study was organized to determine seroprevalence to COVID-19 among the population of the Region.Objective of the study was to determine the level and structure of community immunity to SARS-CoV-2 virus in the population of the Leningrad Region in the period of intensive COVID-19 transmission.Materials and methods. The work was carried out within the framework of the Rospotrebnadzor project on assessment of community immunity to the SARS-CoV-2 virus in the population of the Russian Federation. The content of antibodies to SARS-CoV-2 was determined applying ELISA using a kit for the analysis of human serum or blood plasma for the presence of specific IgG to the nucleocapsid of the SARS-CoV-2 virus , manufactured by the State Scientific Center of Applied Microbiology and Biotechnology (Obolensk) in accordance with the instructions for use.Results and discussion. The study has showed that the herd immunity of the population of the Leningrad Region was 20.7 %. The maximum level has been established in children 1–6 years old (42.3 %) and people over 70 years old (29.0 %). The highest level of seropositivity, except for children and older people, was found among the unemployed (25.1 %). The lowest level of seroprevalence was detected in civil servants (12.8 %) and military personnel (16.7 %). It has been shown that the risk of infection increases by 1.5 times in case of contacts with COVID-19 patients. After exposure to COVID-19 virus, antibodies are produced in 82.1 % of the cases. In individuals with a positive PCR test result obtained earlier, antibodies are detected in 82.8 % of cases. The share of asymptomatic forms among seropositive residents of the Leningrad Region was 86.9 %. The results of assessing the herd immunity to SARS-CoV-2 in the population of the Leningrad Region indicate that during the period of intensive COVID-19 transmission, an average level of seroprevalence was formed. A significant proportion of asymptomatic forms of infection characterizes the high intensity of the latently developing epidemic process. The results obtained should be taken into account when organizing preventive measures, including vaccination, and predicting morbidity rates.

Relevance. Yersinia pseudotuberculosis is a causative agent of pseudotuberculosis, a disease with polymorphism of clinical manifestation that is determined by the presence of specific virulence determinants: plasmid pVM82, pathogenicity islands HPI and YAPI, and superantigen YPM. Occurrence of new determinants depends on horizontal transfer of mobile genetic elements, hence, systems regulating horizontal transfer participate in evolution of pathogenic species. CRISPR-Cas is and adaptive protection system of prokaryotes against mobile genetic elements. Aim. The study analyzed an interaction between CRISPR-loci of Y. pseudotuberculosis and virulence determinants. Results. 86% of strains includes three CRISPR-loci: YP1, YP2, and YP3. Length of locus YP3 mostly depends on presence of virulence determinants in strains of Y. pseudotuberculosis serotype O:1b. Strains with virulence genes are able to cause a severe form of pseudotuberculosis and have longer locus than strains without determinants. Conclusion. Therefore, CRIPSRCas system of Y. pseudotuberculosis may participate in formation of a certain strain genotype that defines clinical manifestation of pseudotuberculosis.

Abstract. The representatives of Y. enterocolitica biotype 1А which are considered as nonpathogenic microorganisms were tested for production of the thermostable enterotoxin YST B (Yersinia Stable Toxin). This toxin is characterized by strong toxic action and it can bring on diarrhea in human and animals. The chromosome gene of thermostable enterotoxin ystB was detected by PCR in 87.1% out of 116 studied strains of different origin and territorial isolation. To determine toxin production in vitro the studied strains cultivated in various conditions: in 26°C and 37°С in usual culture medium and in 37°С in the medium corresponded to the content of intestine. In part of the studied strains the toxin production was revealed on the model of newborn mice in both temperature regimes of cultivation 26°С and 37°С. The study of toxin production in representatives of Y. enterocolitica biotype 1А showed their possible role as etiological agents of diarrhea.