Vol 97, No 5 (2020)

Introduction. In late 2019 - early 2020, an outbreak of infection caused by a novel strain of beta coronavirus SARS-CoV-2 was reported. The World Health Organization defined the disease as coronavirus disease 2019 (COVID-19). In the Tyumen Region, the first case of COVID-19 was diagnosed on 31/1/2020. The source of infection was a female student who came from Jinan, Shandong province (China). The number and rate of cases were steadily increasing from the 16th week through 28th week in 2020. The highest rate was 36.87 cases per 100 thousand people. Afterwards, the cumulative incidence kept increasing gradually, but not as quickly.

The purpose of the seroepidemiological study was to measure the level and to identify the structure of herd immunity against the SARS-CoV-2 virus among the population of the Tyumen Region during the rapid spread of the COVID-19 outbreak.

Materials and methods. Volunteers for participation in the study were selected through questionnaire surveys and random sampling. The exclusion criterion was an active COVID-19 infection at the time of the survey. A total of 2,758 individuals were tested for SARS-CoV-2 specific antibodies. The age of the surveyed volunteers ranged from 1 year to 70 years and older.

Results of the study. During the active phase of the COVID-19 incidence, the population of the Tyumen Region showed moderate (24.5%) seroprevalence of SARS-CoV-2. At the same time, the tests revealed a high (97.8%) rate of asymptomatic infection cases in seropositive individuals who had never been diagnosed with COVID-19 and did not have history of positive PCR test results or acute respiratory infection symptoms on the day of testing. The maximum level of herd immunity was identified in children aged 1-6 years (34.7%), which was significantly higher compared to the average level of seroprevalence in the entire cohort. In recovered COVID-19 patients, antibodies were detected in 68.2%. In individuals with positive PCR test results, antibodies were detected in 64%. Conclusion. The results of the assessment of the level of herd immunity against the SARS-CoV-2 virus are crucial for prediction of the development trend of the epidemic and for planning specific and non-specific COVID-19 prevention measures.

Aim. Study of the sensitivity of Bordetella pertussis biofilms to polyvalent pertussis serum.

Materials and methods. The intensity of biofilm formation by strains of B. pertussis in round-bottomed polystyrene 96-well plates in the presence of polyvalent pertussis serum was estimated by staining with 0.1% gentian-violet solution. The serum titer was estimated as a highest dilution, which suppressed the growth of biofilm cultures.

Results. Serum titers that completely suppressed the formation of biofilms by the studied strains ranged from  : 1,000 to 1 : 20,000. Vaccine strain No. 475a (serotype 1.2.3) was characterized by the highest sensitivity to serum, the titer of which was 1 : 20,000. Vaccine strain No. 305 (serotype 1.2.0) and strains isolated from whooping cough patients in the period from 2001 to 2010: No. 287 (serotype 1.0.3), No. 178 (serotype 1.2.0), No. 317 (serotype 1.2.3) were sensitive to serum in the titers 1 : 1,000-1 : 2,000. Vaccine strain No. 703 (serotype 1.0.3) was resistant to all serum dilutions studied. When sowing supernatants from wells with biofilms on a dense nutrient medium, the growth of colonies typical for B. pertussis was observed. Similar results were obtained when seeding the supernatants of the cultures from the wells with no biofilm.

Conclusion. These data indicate that B. pertussis strains are heterogeneous in sensitivity to pertussis serum. The growth of colonies typical for B. pertussis when culture supernatants are sown on a dense nutrient medium, in the absence of biofilms in the wells, indicates that the biofilm formation is suppressed by inhibiting the adhesion of microbial cells on the substrate, and not due to the bactericidal action of the serum.

Aim. To estimate in vitro the effect of DNA isolated from the probiotic strain Bifidobacterium bifidum 791 on the cell concentration and adhesive properties of fecal isolates of bifidobacteria and opportunistic microorganisms of different species.

Materials and methods. DNA was isolated from the probiotic strain Bifidobacterium bifidum 791. Biomass containing bifidobacteria was washed from the nutrient medium. The suspension of bacteria in the buffer solution was subjected to ultrasonic disintegration with a frequency of 40 kHz three times for 30 minutes, followed by centrifugation. The supernatants were combined and purified chromatographically on CL-4B Sepharose. B. breve, B. bifidum, B. infantis, Staphylococcus aureus, Escherichia coli lac-, Enterococcus faecalis, and Candida albicans were used as test cultures, isolated from the intestines of conditionally healthy adults. 

Results. The nucleic acid solution with a concentration of 3.54 |jg/ml did not affect the cell number of bifidobacteria (p = 0.61). The DNA content in the solution of 14.15-21.23 jg/ml increased the titers of B. bifidum and B. breve by 2 lg CFU/ml compared to the control (p = 0.01), but did not affect the titers of S. aureus, E. coli lac-, E. faecalis, C. albicans (p = 0.73). The DNA solution stimulated the self-aggregation of bifidobacteria in 1.5-2.0 times. The ability to autoaggregate under the influence of bifidobacterial DNA in S. aureus, E. faecalis, C. albicans did not change, in E. coli lacincreased 2.3 times (p = 0.05).

Conclusion. A DNA solution of the probiotic strain B. bifidum 791 with a content 14.15-21.23 jg/ml stimulates the reproduction and autoaggregation of fecal B. breve, B. bifidum.

Since the beginning of the 21th century, major outbreaks of human respiratory syndromes caused by coronavirus infections have caused more than million deaths on the planet. Despite the fact that the first wave of the coronavirus infection took place back in 2002, even now there is not any adequate animal model that would meet the needs of the scientific community for reproducing the pathogenesis, clinical manifestations, immunogenicity, development and testing of preventive and therapeutic compounds specific to Severe Acute Respiratory Syndrome, Middle East Respiratory Syndrome, and Coronavirus Disease 2019 (COVID-19).

The purpose of the study is to provide relevant information on known animal models of human respiratory syndromes caused by coronavirus infections and to focus the reader's attention on their adequacy, which consists in the most accurate imitation of clinical signs and pathomorphological changes.

The review considers the regulatory capabilities of the human microbiota to preserve human health. The problem is not new, but it has expanded with the inclusion of new “findings” since the time of I.I. Mechnikov, a staunch supporter of the useful (protective) function of the normal flora.

The study of the integration of human metabolism and microbes inhabiting human body revealed the participation of microbial metabolites — “signaling molecules” — in providing the homeostasis of the host. Particular attention 

is paid to the metabolic products aromatic amino acids as regulators of the physiological functions of humans and microbes. “Signal” molecules regulate the microbial “quorum”, the immune system (its cellular and humoral components). Opiates, hormonal peptides, in particular, natriuretic hormone, hypothalamic nonapeptides (oxytocin and vasopressin), which have both a direct antimicrobial and an indirect effect in the host's body, are not ignored. Researchers are also showing interest in the products of adipose tissue — “adipokines” (in particular, leptin), which turned out to be a multipurpose regulator showing a pro-inflammatory nature.

The category of “signaling” molecules also includes cytokines that interact with gram-positive bacteria, which is actively discussed in the literature.

In the evaluation of the material presented on various models of infections, a general pattern is observed: under the conditions of symbiosis, a “single regulatory environment” is formed, in which a variety of connections from immediate (direct) interactions are noted, i.e. the destruction of “signaling” molecules, induction of physiological functions due to the presence of similar receptors with ligands and, finally, modification of “signaling” molecules, i.e. expansion of the spectrum of action. The combination of this variety of integration mechanisms in this “single regulatory environment” (microorganism-host) probably leads to the formation of homeostasis, i.e. dynamic balance of the “signaling” systems of the microbiota and humans in the conditions of associative symbiosis, where an infection is its model system.

This concept fits well our method of intermicrobial recognition of friend-foe in the dominant-associate pair and the described triangle: microbiota-hypothalamic-pituitary neurosecretion-oxytocin, organically constituting the gut-brain axis.

The review analyzes literature data on the phenotypic variability of Vibrio cholerae of the O1 serogroup. Three types of polysaccharide structures are distinguished in the cholera pathogen: lipopolysaccharide, or O-antigen, capsular polysaccharide and exopolysaccharide. The rugous form of V. cholerae strains is able to synthesize exopolysaccharide which is highly resistant to antimicrobials, and to form wrinkled colonies that can be agglutinated with cholera sera in various combinations. Serological classification of V. cholerae is based on the specificity of the lipopolysaccharide. V. cholerae of serogroups O1 and O139 causes cholera epidemics, although strains from non-O1/non-O139 serogroups with the main virulence factors are known. Upon transition from the Sto the R-form, lipopolysaccharide loses the O-polysaccharide, and the central region begins to fulfill the function of somatic antigen, exhibiting R-specificity. The serological differences in the strains of V. cholerae are based on a change in the regulation or structural organization of genes encoding the biosynthesis of O-antigen (rfb). From 1988 to 2019, 168 strains of V. cholerae that are atypical for agglutinability and were isolated from the R variant were isolated from environmental objects in the territory of the former USSR and subjects of the Russian Federation; the genetic organization of these strains has not been fully studied. The evolutionary relationships of atypical strains of cholera vibrios isolated from environmental objects in Siberia and the Far East are determined on the basis of a comparative analysis of housekeeping genes. The analysis of the results of basic and applied research indicates that the problem of variability in agglutinability of V. cholerae strains isolated from humans and from environmental objects remains relevant at the current stage of development of the seventh cholera pandemic. The atypicality of strains of V. cholerae O1 on this basis is considered in aspects of the environmental conditions of their existence and the conditionality of phenotypic manifestations by molecular biological determination.

Introduction. One of the reasons for the increase of pertussis in the Russian Federation on the background of the widespread coverage of prophylactic vaccinations of more than 95% is a large number of unreasonable medical recusals and parental refusals and, as a result, untimely prophylactic vaccinations against pertussis infection.

Materials and methods. We analyzed 5101 emergency notifications for pertussis in children under 17 years of age in Moscow in 2012-2017 and 300 child development histories for children under 14 years of age in two clinics in Moscow. A сase-сontrol study was conducted to assess the relationship between pertussis and the presence of deviations in the immunization schedule.

Results. It was found that the level of timely immunization against pertussis did not exceed 5%. Medical (20%) and parental refusals (45%) prevail among the reasons for delayed vaccination. In the structure of medical exemption, the main causes are perinatal encephalopathy, congenital heart defects, intestinal dysbiosis, allergic diseases, anemia and some chronic diseases.

Discussion. The main principle for the formation of a full protective immunity from pertussis infection is the mandatory administration of a full primary course of vaccination against pertussis, with the completion of three vaccinations at the age of 10-12 months and mandatory control over the timely receipt of a booster dose no later than the child reaches two years of age. In addition, it is necessary to introduce additional booster doses of pertussis vaccine at the age of 6-7 years, 12-14 years, vaccination of adults every 10 years, as well as consider the introduction of vaccination of expectant mothers in each pregnancy at 27-36 weeks, vaccination for medical personnel and employees who provide child care services.