At the current level of scientific knowledge about the organization of biological systems, the role of microorganisms in their functioning seems quite evident. However, the significance of microorganisms and the role of disturbances in microecology in the development of somatic pathologies remains a subject of debate and discussion. This review article is dedicated to explaining the author’s position regarding the current prospects for using microorganisms as a means of correcting dysbiotic conditions. It discusses both the use of foreign microorganisms in the form of probiotics or fecal transplants, and the prospect of using one’s own, indigenous bacteria to restore the individual microbial ecology of humans and animals.

Research and publications over the past decade have radically changed traditional medical concepts and our understanding of the possible relationship between organs and body systems. So, many studies are devoted to the study of the relationship between the intestinal microbiome and various diseases. The microbiome of the oral cavity has a certain effect on the intestinal microbiome. This review, based on published sources from the Pubmed and Scopus databases, which examined the relationship between periodontal microbiota/periodontal diseases and gastroenterological diseases, presents an expanded version of the report at the round table of the Scientific Society of Gastroenterologists of Russia on June 20, 2025. Within the framework of the hypothetical “journey” of the periodontal microbiota on the “periodontal-gastroenterological express” along the route mouth-intestine, the possible influence of the periodontal microbiota and periodontal diseases on the development of gastroenterological diseases is considered. The results of epidemiological, experimental and clinical studies indicate that periodontopathic bacteria can participate in the development of cancer of the gastrointestinal tract, peptic ulcer, inflammatory bowel disease and non-alcoholic fatty liver disease.

Objective. To study the dynamics of human intestinal microbiota under conditions of artificial isolation (simulating space flights) using a new eubiotic index that evaluates the balance of opportunistic and opportunistic microorganisms. Materials and methods. Data: archival materials of the Soviet space programs (1960-1980) and modern isolation experiments (“Sphinx”: 60 days; “Sirius”: 120/240 days; “Mars-500”: 520 days). Methodology: classical seeding on nutrient media to count microorganism colonies. Index I: calculated based on the priority of bacterial colonization. Statistical processing: Shapiro-Wilk, Kruskal-Wallis, ANOVA, Dunn test (StatTech v3.0.9 and R programs). Results. Short-term isolation (up to 15 days): Peak of the eubiotic index on days 8-11 with subsequent decrease (approximation: R² = 0.9986). Long-term isolation (60-520 days): Steady decrease in the eubiotic index I, reaching a minimum on days 150-300 (I < 1 - dominance of opportunistic microflora). Probiotics slow down, but do not prevent dysbiosis. Model verification: good agreement with the Sphinx experiment. Conclusion. Isolation causes a decrease in the diversity of microbiota and a shift in the balance towards opportunistic microorganisms. The following are recommended for long-term space missions: integration of prebiotics into the diet; personalized probiotics.

Ulcerative colitis (UC) is characterized by pronounced dysbiosis of the gut microbiota, with previous studies implicating multiple bacterial taxa in disease pathogenesis. This study investigated the species-level diversity of Blautia in 24 UC patients and 15 healthy controls (HC) using 16S rRNA gene sequencing and MALDI-TOF mass spectrometry for species identification. Results demonstrated a marked 10.9-fold increase in Blautia abundance in UC patients (mean 44.6% vs. 5.26% in HC, p=0.0003), with four species - B. obeum, B. luti, B. faecis, and unidentified Blautia sp. (ID 375)-accounting for >80% of the genus. Notably, B. luti showed 100% prevalence in UC patients versus 79.2% in HC (p=0.0086). This Blautia expansion paradoxically correlated with reduced abundance of protective bacteria, including Faecalibacterium duncaniae, Anaerostipes hadrus, and Dorea longicatena, and was associated with increased disease severity. Although Blautia species are known butyrate producers with anti-inflammatory properties, their overabundance in UC represents functional dysbiosis, in which the microbiota attempts metabolic compensation but fails to effectively deliver short-chain fatty acids in the pathologically altered colonic environment. The concurrent depletion of mucus-layer-associated bacteria indicates compromised intestinal barrier integrity. These findings establish Blautia diversity as a potential marker of dysbiosis for UC severity, opening new diagnostic and therapeutic avenues for disease stratification and targeted interventions aimed at restoring eubiotic composition through selective bacterial modulation.

Introduction. The intestinal microbiome has attracted much attention from scientists worldwide due to its complex interaction with many diseases, including obesity, metabolic disorders, and cardiovascular diseases. Objective: to study the state of the small intestinal microbiome in adolescents with constitutional-exogenous obesity and lipid metabolism disorders. Materials and methods. A one-time case-control study was conducted on 50 adolescents aged 12-17 years with constitutional-exogenous obesity of grades 2-4 living in St. Petersburg. Complaints, life history data and disease, objective clinical examination, and laboratory and instrumental research results were assessed. In particular, special attention was paid to the analysis of the lipidogram. The state of the parietal microbiota of the small intestine was studied by the method of blood gas chromatography-mass spectrometry (MSMM) (according to the author’s method of Osipov G.A.). Statistical data processing was carried out using the IBM SPSS Statistics 27.0 program (USA). Results and discussion. Analysis of the quantitative composition of the small intestine microbiome showed that there was a redistribution of phylotypes. It was characterized by a general decrease in the number of all identified bacteria and the predominance of Firmicutes microorganisms. Moreover, with hypercholesterolemia, an increase in clostridium propionicum, lactobacillus spp and lactococcus spp was noted, and with hypertriglyceridemia, a decrease in micromycete spp (sitosterol). Our data were comparable with the results of work conducted by scientists from China. However, a number of foreign studies have shown that lactobacilli contribute to a decrease in the level of total cholesterol, LDL. This problem requires further study. Conclusion. In adolescents with obesity and dyslipidemia, the microbiome of the small intestine was found to have a decreased diversity and a predominance of Firmicutes microorganisms, a decreased amount of micromycete spp (sitosterol).

Periodontal diseases are considered to be among the most prevalent diseases (up to 95%) in patients of dental clinics. The involvement of the oral microbiota in the development of this pathology, the insufficient number of studies of the state of the oral cavity and colon microbiocenoses in periodontitis, as well as the potential therapeutic benefits of probiotics in the in prevention and treatment of periodontitis have determined the relevance of this work. The objective of the present study was to investigate in-depth the oral cavity and colon microbiota of patients with chronic generalized periodontitis and to develop an algorithm of the use of probiotic dietary supplement probiotic complex of bifidobacteria and lactobacilli based on 6 strains belonging to the species Bifidobacterium bifidum, Bifidobacterium longum, Lactobacillus plantarum, Lactobacillus fermentum on enterosorbent zeolite in the combined therapy of periodontal diseases. To study the species composition of the microbial communities of these loci, we used a bacteriological method for isolating pure cultures, followed by the identification of microorganisms by MALDI TOF mass spectrometry. The hygiene index, the Muhleman bleeding index, and the associated periodontal index were used for clinical assessment of the periodontal condition. To correct the microbiota in both biotopes, the author’s probiotic containing Lactobacillus and Bifidobacterium species immobilized on zeolite was used. As a result of the conducted research, we discovered, identified and determined the count of a wide range of oral bacteria, including periodontopathogens, such as orange complex bacteria: in 10.3% of patients Prevotella nigrescens in the amount of 10 3-10 7 CFU/ml, in 45.8% - Fusobacterium nucleatum in an amount of 10-1 -10.5 CFU/ml. It was found that chronic generalized periodontitis of moderate severity is accompanied by pronounced (48.5%) and most pronounced (25%) oral microbiota dysbiosis as well as dysbiotic changes in the colon of the first (50%) and second (33.3%) degrees. After the treatment according to our proposed algorithm, we recorded an improvement in clinical (decreased bleeding, good hygiene) and microbiological parameters in the main group - the typical orange complex periodontopathogens ceased to be isolated, normalization of the microbiocenoses of the oral cavity and colon occurred in 73.5% cases versus 15.7% in the comparison group. The proposed therapy method is protected under patent No. 2789345 dated 02.01.2023 “Method of treatment of chronic generalized periodontitis of moderate severity in patients with comorbid pathology”.

The aim of the research. To determine the number of Helicobacter pylori (H. pylori) infected people and genotypic resistance to clarithromycin in residents of the Transbaikal region and medical staff using molecular genetic testing, to analyze the effectiveness of eradication in case of genotypic resistance. Materials and methods. 240 residents of the Transbaikal region were examined, including 58 medical and 182 non-medical staff. In biopsies obtained during gastric endoscopy, H. pylori DNA and mutations A2142G, A2143G, T2717C associated with resistance to clarithromycin were determined. Eradication with clarithromycin was performed in 35 people. Eradication control was performed 6-8 weeks after treatment by determining the H. pylori antigen in feces. Statistical methods: descriptive statistics, unpaired Student’s t-test, x2-test, odds ratio (OR) (Biostatistics). Results. H. pylori DNA was detected in 40.8% (CI: 37.6-44.0%) of individuals, 58.6% in medical staff, and 35.2% in non-medical workers (p=0.002). Mutations A2142G and/or A2143G were detected in 38.8% (52.9% in physicians, 31.2% in non-medical workers, p=0.036). The OR of the presence of H. pylori DNA in medical staff was 2.612 (95% CI: 1.427-4.782), and the presence of mutations A2142G and/or A2143G was 2.475 (95% CI: 1.051-5.826). Successful eradication was 62.8%. In individuals with Helicobacter pylori mutations, the effective treatment was 41.2%, in those without mutations - 83.3%. The OR of effective therapy in individuals with A2142G and/or A2143G mutations was 0.140 (95% CI: 0.029-0.674). Conclusion. The prevalence of H. pylori in the Transbaikal region was 40.8% in a genetic study. A high proportion of clarithromycin-resistant Helicobacter pylori strains was detected - 38.8%. Medical staff have higher rates of H. pylori, including resistant strains. In the presence of clarithromycin-resistant H. pylori, the effectiveness of eradication was reduced by 2 times. Before prescribing H. pylori eradication therapy including clarithromycin, it is advisable to test for H. pylori mutations, especially in medical staff.

The aim of the study to evaluate the incidence of H. pylori infection in men aged 18-26 years (conscripts and conscripts) with symptoms of dyspepsia in 2010-2013 and in 2020-2023, to determine the primary resistance of H. pylori to clarithromycin in 2024. Materials and methods. The results of the study of the frequency of H. pylori in men aged 18-26 years, performed in 2010-2013 and in 2020-2023, the results of the study of primary H. pylori resistance to clarthromycin in 2024. Results. The incidence of H. pylori infection in men aged 18-26 years with symptoms of dyspepsia in 2010-2013 was 61.2% among conscripts (95% CI 52.1-69.6), 65.3% among conscripts (95% CI 59.1-71.1). In 2020-2023, compared with 2010-2013, there was a statistically significant decrease in the incidence of H. pylori in men aged 18-26 years (conscripts) with dyspepsia from 65.3% (95% CI 59.1-71.1) to 49.3% (95% CI 45.3-53.2; χ2 = 17.69; p < 0.001). In 2020-2023, H. pylori in the presence of dyspepsia, in contrast to the period 2010-2013. It was more often detected in conscripts from rural settlements (57.6%; 95% CI 49.5-65.4) compared with conscripts from cities (46.7%; 95% CI 42.2-51.2; χ² = 5.31; p < 0.02). Primary H. pylori resistance to clarithromycin in men aged 18-26 (conscripts) in 2024 was determined by molecular genetic analysis in 13.6% (95% CI 8.3-21.5). Conclusion. Over a ten-year period, the prevalence of H. pylori infection in men aged 18-26 years (conscripts) with dyspepsia decreased.

Chronic gastroduodenitis (CGD) is considered as a multifactorial pathology, in the etiology of which the leading role is assigned to infection with H. pylori (HP). The issue of symbiotic relationships of HP with other infectious agents, including pathogens of parasitic and fungal nature, is being discussed in the scientific community, but the features of combined lesions are insufficiently described. The aim of the study was to study the frequency of H. pylori and protozoal fungal invasions in chronic inflammatory diseases of the stomach and duodenum, the effect on morphological changes in the mucous membranes of the gastrointestinal tract. Material and methods. 87 patients diagnosed with CGD were examined. The material for the study was biopsies of the gastric mucosa and duodenum 12, faeces. Cytological and immunochromatographic methods were used to identify HP. The staining by Romanovsky-Giemsa was used for detection of the morphological changes in the mucous membranes and the microflora. Parasitoscopic methods were used to identify the protozoa. The results of the study. When studying the microbial composition of the stomach in 87 patients with CGD, the mixed microflora was found, including eukaryotic nature. A preliminary analysis of the results in the group of H. pylori-positive patients (n=57) showed that the association of H. pylori and yeast-like fungi of the genus Candida was found in 29% of cases, the association of H. pylori, yeast-like fungi of the genus Candida and protozoa (G. lamblia) - in 19% of cases. The study of the SOF microflora of patients with CGD showed the presence of more severe forms of morphological changes, in particular, intestinal metaplasia and dysplasia, in H. pylori and fungal-protozoal mixed invasion, than in the absence of infection (p<0.05). A significant difference was noted in the group of H. pylori -positive for the detection of protozoa and fungi of the genus Candida compared with the group of H. pylori-negative patients (p<0.05). Conclusion. The presence of protozoal fungal mixed invasion in H. pylori - associated with the gastroduodenitis can have a potentiating pathogenetic effect on the functions of all parts of the gastrointestinal tract, leading to dysbiotic disorders and the development of a chronic inflammatory process, which requires the development of algorithms for complex diagnosis and correction of dysbiotic conditions.

The article presents a comprehensive review that systematizes current data on extragastric manifestations of Helicobacter pylori infection. In addition to the well-established association of the microbe with gastrointestinal pathologies (gastritis, ulcer, gastric cancer), H. pylori can persist in other organs and exert a systemic negative influence on the body. The article examines four main pathways for the development of extragastric manifestations during the persistence of the microorganism: direct migration of the bacteria and colonization of other organs, the development of chronic systemic inflammation and endotoxinemia, the phenomenon of molecular mimicry leading to autoimmune reactions, and an indirect influence through disruption of the gut microbiota (dysbiosis). It is emphasized that Helicobacter pylori infection and intestinal dysbiosis are links in the same pathogenetic chain. Eradication therapy can exacerbate dysbiosis, highlighting the potential benefit of using probiotics.

Purpose of the study. To draw the attention of gastroenterologists to the high intensity of intragastric acid production as a factor that can reduce the clinical effectiveness of macrolide antibiotics prescribed both for the eradication of H. pylori and for other indications. Materials and methods. A review of published data was performed with general information on macrolides, information on their comparative acid resistance, methods of protecting active substances from the effects of the acidic environment of the stomach and the reasons for the failure of this protection. Results of the study. Among the widely used macrolides, roxithromycin is the most acid-resistant. Erythromycin, rarely prescribed as a prokinetic, is produced in dosage forms with enteric coatings. Clarithromycin, which has average acid resistance, is prescribed with PPIs for the eradication of H. pylori. It is known that the resistance of H. pylori to clarithromycin, caused mainly by the presence of nucleotide substitutions in the binding region of macrolide antibiotics in the 23S molecule, has reached 28.9% in some regions of the world. Some researchers have noted that the intensity of the antisecretory effect of PPIs depends on the individual characteristics of the patient’s metabolism using CYP2C19. According to our data, clarithromycin may be partially destroyed in an acidic environment if it is used together with PPIs in dosage forms with poor-quality enteric coatings that can be destroyed under conditions of fulfilled Bell’s rule or under the influence of pathological duodenogastric reflux. This factor has been demonstrated by experimental data. Conclusion. Current clinical practice does not take into account the relationship between the chemical and pharmaceutical properties of macrolides and the drugs used together with them, with their clinical efficacy, namely: When prescribing macrolides in oral dosage forms, their comparative acid instability and the likely presence of conditions in patients associated with high intensity of intragastric acid production should be taken into account; The ineffectiveness of H. pylori eradication when using triple therapy with clarithromycin may be associated not only with the resistance of the pathogen to the macrolide, but also with instability in the acidic environment of enteric-coated forms of simultaneously prescribed proton pump inhibitors.

Medications, especially those taken orally, inevitably come into contact with microorganisms inhabiting the gastrointestinal tract (GIT). The intestinal microbiota can produce enzymes with various catalytic activities and, thus, affect the biological activity, bioavailability and toxicity of several natural or synthetic substances, including medicines, as well as biotransform drugs into other chemical forms or metabolites that can alter the effectiveness or toxicity of the initial active substance. The intestinal microbiota can also indirectly influence the effectiveness and toxicity of drugs by altering the body’s ability to metabolize or the processes occurring in the body (affecting liver function, altering the expression of liver enzymes or metabolic genes, interfering with detoxification processes). On the other hand, drugs like xenobiotics can have a negative effect on the microorganisms of the gastrointestinal tract, which can contribute to the development of side effects from the digestive system. The article discusses possible interactions between the intestinal microbiota and nonsteroidal anti-inflammatory drugs.

Hyperhomocysteinemia is a common obstetric complication. Currently, the relationship between homocysteine levels and the composition of the intestinal microbiota is of particular interest to researchers. The role of intestinal microbiota is currently being studied in many physiological and biochemical processes in the human body, including pathology. In the context of methionine metabolism, microbiota can participate in the regulation of methionine cycle reactions, as well as in the metabolism and absorption of vitamins. Pathological microbiota that occurs with hyperhomocysteinemia can contribute to the development of conditions that pose a threat to pregnancy. The interdependence of intestinal microbiota, hyperhomocysteinemia and concomitant obstetric complications is important for the diagnosis and treatment of these diseases and is of interest to the scientific community.

Purpose. Study of biotechnological potential of strains of the BIOTROF company collection using whole-genome NGS sequencing. Material and methods. The genome of 6 bacterial strains of the genera Bacillus, Lactobacillus and Streptococcus from the collection of BIOTROF LLC (St. Petersburg) was analyzed. Bioinformatics data analysis included processing in software packages of tools and databases RAST, KEGG Pathway, antiSMASH 6.0, Norine, CAZy, PHASTER, VirulenceFinder and ResFinder. Results. The analysis showed that the studied strains had genes associated with the synthesis of a large number of antimicrobial substances of various natures and spectrums of action, enzymes, vitamins, amino acids, genes of resistance to aggressive environmental factors and other properties that determine the high potential of their application in various industries. The use of strains of the genus Bacillus and Enterococcus may be more preferable for the production of biopreparations for plant growing (stimulation of plant growth and protection, bioremediation) and animal husbandry (regulation of the gastrointestinal microbiome, increased immunity, detoxification, increased availability of nutrients) due to a wider range of genes associated with adaptation, enzymatic activity, antimicrobial protection, synthesis of vitamins and amino acids. Lactobacillus plantarum 600, Bacillus subtilis 111, Bacillus mucilaginosus 159 in the genome have determinants of osmotolerance and synthesis of antimicrobial compounds, which determines their potential as preservatives for feed, and Streptococcus thermophilus L has genes for the synthesis of exopolysaccharides necessary for the production of fermented milk products. The genome of all the studied strains did not contain elements that contribute to the formation of toxic and virulent properties of the strains. Conclusion. The studied strains have been shown to have high potential for use in crop production, livestock farming and the food industry.

Anxiety disorders remain a significant problem among older adults and impact their quality of life, physical health, and psycho-emotional well-being. This study conducted an analysis of both literature and own data on psycho-emotional characteristics, particularly anxiety levels and microbiota composition in individuals suffering from age-associated diseases (metabolic syndrome, obesity, diabetes mellitus, dyslipidemia, hypertension, atherosclerosis). Patients with metabolic syndrome were divided into three groups based on psychometric analysis of personal anxiety. Personal anxiety was assessed using the Spielberger scale, which classified participants into low (LT1, < 30 points), moderate (LT2, 35-45 points), and high (LT3, > 45 points) anxiety levels. Waist circumference, serum alkaline phosphatase, and insulin levels tended to be higher or were statistically significantly increased in the LT2 and LT3 groups compared to LT1. Additionally, with increasing levels of personal anxiety, the quantitative content of Escherichia coli and bacteria from the Bacteroides fragilis group decreased. A negative correlation of moderate strength was found between the severity of personal anxiety and the abundance of these bacteria. Based on the findings of this study and existing literature data, the presence of a compensatory psychobiotic effect of E. coli and B. fragilis in elderly patients cannot be ruled out.

The effect of probiotic and autoprobiotic (indigenous non-pathogenic) E. coli on intestinal motility and microbiota in experimental intestinal dysbiosis in male Wistar rats was studied. The administration of ampicillin and metronidazole led to a decrease in appetite, weight loss, and diarrhea. In animals with intestinal dysbiosis, there was a decrease in the amplitude of intestinal wall contractions and the amount of work performed by the smooth muscle cells of the intestinal wall, compared to the control group of intact animals (K2), accompanied by an increase in the population of Klebsiella and Bacteroides fragilis group. In contrast to the control group K1, which did not receive any treatment for dysbiosis, the administration of probiotic and autoprobiotic E. coli resulted in a decrease in the number of opportunistic pathogens and an increase in the number of fecalibacteria (butyrate producers). Changes in the microbiota contributed to the restoration of motor activity in the distal colon of rats.

Multiple sclerosis (MS) is a chronic autoimmune disorder of the central nervous system, characterized by inflammatory demyelination and neurodegeneration. Increasing attention has been directed to the “microbiota-gut-brain” axis, as intestinal barrier dysfunction and alterations in gut microbiota composition have been reported to precede the clinical onset of MS, although their association with disease severity remains uncertain. Experimental autoimmune encephalomyelitis (EAE) in rodents is a well-established model that reproduces the key immunological and morphological features of MS. However, comparative investigations addressing both the taxonomic structure of the microbiota and intestinal morphological changes across different severities of EAE remain scarce. To compare the taxonomic composition of the gut microbiota and structural alterations of the intestinal epithelium in rats with different severities of experimental autoimmune encephalomyelitis (EAE). The study was conducted on 39 female Wistar rats (intact, n=9; EAE-induced, n=30). EAE was induced by a single subcutaneous injection of spinal cord homogenate in complete Freund’s adjuvant. Morphological and ultrastructural changes in the intestinal epithelium were assessed using histological techniques and electron microscopy. The taxonomic composition of the gut microbiota was analyzed by 16S rRNA gene sequencing. When comparing the intestinal microbiome of mildly and severely ill rats, significant differences were observed in the representation of 4 phyla: Bacillota, Bacteroidota, Actinomycetota and Cyanobacteriota. In the baseline microbiome of severely affected rats, the abundance of the class Epsilonproteobacteria (Pseudomonadota) was increased. Clinical symptoms developed in both groups against the background of a decreased number of Bacteroidota (family Prevotellaceae). During the recovery phase, the abundance of Bacteroidota was restored only in mildly affected and recovered animals, whereas in rats with severe EAE the proportion of Actinomycetota increased. At the genus level, distinct group-specific dynamics during EAE were identified for 9 genera (unclassified Clostridiaceae and Peptoscreptococaceae, Allobaculum, Turicibacter, Prevotella, Parabacteroides, Desulfovibrio and Bifidobacterium). Alongside more pronounced alterations in the gut microbiome, rats with severe EAE displayed significant morphological changes in the intestine. At the peak of the disease, leukocyte infiltration of the mucosa, reduction in goblet cells numbers, shortened and thickened small intestinal villi and decreased crypt depth in the colon were observed, all correlating with the severity of the disease. Ultrastructural analysis further revealed mitochondrial and microvilli damage in enterocytes and colonocytes, which was more pronounced in severely affected animals. These findings support the involvement of the “microbiota-gut-brain” axis in the development of autoimmune demyelinating CNS disorders. The observed association between intestinal morphological alterations, gut microbiota composition, and EAE severity highlights the potential of targeting intestinal inflammation and barrier function for therapeutic strategies in multiple sclerosis

The effect of autoprobiotics, indigenous nonpathogenic enterococci, and the indigenous consortium of microbes (ICM) obtained from fecal samples on the restoration of intestinal microbiocenosis and behavioral responses in male Wistar rats with intestinal dysbiosis induced by ampicillin and metronidazole was studied. The conditions used for fecal sample cultivation led to an increase in the proportion of lactobacilli and enterococci in the ICM. When analyzing the condition of animals, in particular, when evaluating motor and exploratory activity in the “open field” test, as well as the results of 16S rRNA sequencing after administration of autoprobiotics, the following were revealed: faster disappearance of dyspepsia, decreased signs of anxiety, and compensatory changes in the composition of the microbiota. The composition of the intestinal microbiome had significant differences in the animal groups depending on exposure after administration of antimicrobial drugs. Moreover, in the group that did not receive autoprobiotics, along with more pronounced signs of dysbiosis, signs of self-healing were revealed. The maximum changes in the intestinal microbiota and the effect on animal behavior were exerted by ICM. The revealed phenomena should be taken into account when developing methods of complex therapy of diseases accompanied by the development of dysbiotic conditions, especially with pronounced changes in the functioning of the central nervous system.

Objective: To conduct a comprehensive assessment of the effect of Lactobacillus acidophilus LA-5 and Bifidobacterium animalis subsp. lactis BB-12 strains on the gut microbiota of a child with dysbiosis using a human artificial gastrointestinal (GI) tract model. Materials and Methods: The study was conducted using an automated, three-reactor artificial gastrointestinal tract system simulating the stomach, duodenum, and large intestine. The microbial community was formed from fecal samples of a child with third-degree dysbiosis. The probiotic product Linex Forte was then administered for 14 days. Microbiota composition was analyzed by real-time PCR, and metabolic activity was assessed by the content of organic acids using GC-MS (gas chromatography-mass spectrometry). Results: The combination of Lactobacillus acidophilus LA-5 and Bifidobacterium animalis subsp. lactis BB-12 strains demonstrated a pronounced corrective effect on dysbiotic disorders of the gut microbiota in the artificial GI model. The restoration of lactobacilli populations to 9.0 log CFU/mL and bifidobacteria to physiological norms was recorded. Elimination of opportunistic microorganisms (Citrobacter spp., C. perfringens) was observed by days 7-9. The Bacteroides spp. / F. prausnitzii ratio normalized from 74.1 to the optimal range of 16.9-38.8. Chromatographic analysis revealed specific patterns of metabolic activity of the strains with the restoration of a normal organic acid profile, including the accumulation of lactic and succinic acids. Conclusion: The study confirmed the comprehensive positive impact of the LA-5 and BB-12 strain combination on the key parameters of the gut microbiome in dysbiotic conditions, resulting in a significant prolonged effect. The persistence of the achieved results after the completion of the product's administration indicates the formation of a stable population of probiotic microorganisms, which is of fundamental clinical importance for achieving a long-term therapeutic effect.