This bibliographical review provides an analysis of modern domestic and foreign sources on the microbiome of the upper respiratory tract (URT) in children of early and preschool ages. It was discovered using the genetic sequencing method that the mucous membranes of the URT are inhabited by a wide range of bacteria belonging to the genera Firmicutes, Actinobacteria, Bacteroidetes, Proteobacteria and Fusobacteria, with the predominant genera Moraxella, Haemophilus, Streptococcus, Flavobacteria, Corynebacterium and Neisseria. Colonization of the URT begins at birth and continues into the first 3 years of a child's life. It is influenced by the method of delivery as well as the environmental microbiome in the baby's environment. Normal microbiota has colonization resistance, prevents the colonization of pathogenic flora, and also competes with pathogens. It has been proven that microbiota profiles in infants and preschool children vary depending on the season. One of the important areas of research is the assessment of the impact of antiseptics and antibiotics, as well as probiotic preparations, on the microbiota.

Introduction. The microbiota of the upper airways and intestine in preschool children is directly involved in protecting the growing body from acute respiratory infections (ARI), which are the most common infections in children, about 65% of them turn into recurrent respiratory infections (RRI). Aim. To establish changes in the microbiota of the upper airways and intestine in the treatment of ARI in preschool children. Materials and methods. The study involved sixty 1–6 year (Me = 3.38 years) frequently ill children. They were divided into 3 groups depending on the chosen treatment lasting 90 days. Children of group 1 (n = 20) underwent nutrition correction. Children of group 2 (n = 20) received additional probiotics. Children of group 3 (n = 20) received both nutritional correction and probiotics at the prescribed doses. Before and after treatment, the composition of the microbiota of the oropharyngeal zone and intestine was determined by genetic sequencing of the V3–V4 region of the 16S ribosomal RNA gene, followed by bioinformatic analysis. Results. Significant differences were found mainly in the relative content of Firmicutes in the microbiota of patients treated. The content of Firmicutes in the microbiota of children receiving probiotics against the background of nutrition correction (30%) was significantly higher than in patients with nutrition correction (26.91%) and in children receiving only probiotics (25.95%). In patients of different groups, after treatment, a decrease in the content of Proteobacteria in the microbiota of the oropharyngeal zone was revealed. A significant decrease in the relative content of Bacteroidota (by more than 3 times) in 95% of patients, and a decrease in Proteobacteria (by more than 4.5 times) in 100% of patients was also found in the intestinal microbiota of group 3 patients treated with probiotics. In addition, there was a significant increase in the Firmicutes microbiota from 21.97% to 30.07% in 85% of patients, and an increase in the content of Actinobacteriota from 1.9% to 5.7% in 95% of patients. The relative content of undifferentiated microbiota after therapy was also significantly higher (70.08%) than before treatment (58.40%) in 85% of patients.

Respiratory infections are one of the leading diseases currently and almost 2/3 of these infectious processes occur in childhood. The pathogenesis of recurrent respiratory infections is based on the failure of the links of the immune system, mainly caused by a violation of the immune homeostasis of the mucous membranes of the nasopharynx and oropharynx. The purpose of this research was to determine the effect of the immunomodulatory therapy using sodium deoxyribonucleate on the microbiota of the oropharynx in children with recurrent respiratory infections. A single-center randomized placebo-controlled closed experimental study was performed in 90 pediatric patients with recurrent respiratory infections aged 1 to 6 y/o in May 2021-Nov. 2021 on the basis of the private medical center “Center for Modern Pediatrics” located in Voronezh, Russia. The main group consisted of 46 (23 boys and 23 girls aged 4 [3; 5] y/o) who had been given the sodium deoxyribonucleate drug nasally for 30 days. The control group of 44 (22 boys and 22 girls aged 4 [3; 5] y/o) had been given a placebo (a sterile 0.1% sodium chloride fluid) according to the same prescription scheme. The concentration of secretory immunoglobulin was determined by the enzyme immunoassay; the composition of the microbiota was studied by the genetic sequencing of the 16S ribosomal RNA gene. All of the participants in both groups were examined twice: at the start of the study and 90 days after. A statistically significant decrease in the relative amount of Proteobacteria and an increase in the relative amount of Firmicutes and Actinobacteriota, an increase in the concentration of sIgA was found against the background of the use of the drug, which in tis turn indicates an increase in the activity of mucosal immunity (p<0.001). Conclusion: thus, the use of sodium deoxyribonucleate in children aged 1 to 6 years old with recurrent respiratory infections leads to a statistically significant decrease in the relative amount of Proteobacteria and an increase in the relative amount of Firmicutes and Actinobacteriota in the oropharynx; increased activity of mucosal immunity, as evidenced by an increase in the concentration of sIgA.