ASSESSMENT OF INTESTINAL MICROBIOCENOSIS IN PATIENTS WITH IRRITABLE BOWEL SYNDROME: DYSBIOTIC PATTERNS, DIAGNOSTIC APPROACHES, AND THERAPEUTIC IMPLICATIONS

Background: Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder affecting 10–15% of the global population, characterized by recurrent abdominal pain associated with altered bowel habits. Accumulating evidence from metagenomics, metabolomics, and microbial culture studies has established that intestinal microbiocenosis—the complex community of microorganisms inhabiting the gastrointestinal tract—is profoundly disturbed in IBS patients compared to healthy controls. This gut dysbiosis is now considered a central pathophysiological mechanism rather than an epiphenomenon, linking intestinal microbiota alterations to visceral hypersensitivity, epithelial barrier dysfunction, immune activation, and brain-gut axis disturbance. Objective: To systematically evaluate the composition and functional characteristics of intestinal microbiocenosis in IBS patients across subtypes, to analyze the available diagnostic methodologies for gut microbiota assessment, and to review microbiota-targeted therapeutic strategies with clinical efficacy data. Methods: A systematic review of eight primary peer-reviewed sources was conducted, encompassing meta-analyses, prospective cohort studies, randomized controlled trials, and authoritative clinical guidelines published between 2006 and 2024. Results: IBS patients demonstrate consistent reductions in Bifidobacterium, Lactobacillus, Faecalibacterium prausnitzii, and Akkermansia muciniphila alongside increases in Proteobacteria (Escherichia, Klebsiella), Ruminococcus gnavus, and Clostridium species compared to healthy controls. The Firmicutes/Bacteroidetes ratio is elevated in IBS-C and reduced in IBS-D subtypes. Metagenomic sequencing (16S rRNA amplicon sequencing and shotgun metagenomics) provides superior taxonomic resolution over culture-based methods, with alpha-diversity consistently reduced (Shannon index reduced by 0.3–0.8 units) and beta-diversity significantly altered in IBS cohorts. Microbiota-targeted interventions—rifaximin (non-absorbable antibiotic), multi-strain probiotics, and low-FODMAP diet—demonstrate clinical efficacy for global IBS symptom relief and partial microbiome normalization. Conclusion: Gut dysbiosis is a reproducible finding in IBS that is mechanistically linked to the syndrome's cardinal symptoms through multiple pathways. Microbiocenosis assessment using next-generation sequencing combined with metabolomic profiling offers the most comprehensive characterization of the IBS-associated dysbiotic phenotype, paving the way for precision microbiome-targeted therapeutics.