Small Intestinal Microbial Overgrowth (Sibo, Imo, and Sifo) in the Pathogenesis and Management of Irritable Bowel Syndrome

Background. Irritable Bowel Syndrome (IBS) is a complex functional disorder characterized by abdominal pain and altered bowel habits. Small Intestinal Bacterial Overgrowth (SIBO) is increasingly recognized as a key pathogenetic factor, shifting the understanding of IBS toward a micro-organic basis. IBS is viewed as a heterogeneous condition with distinct phenotypes: microbiota-driven, post-infectious (PI-IBS), centrally mediated, and genetic variants. Aim. To evaluate the role of SIBO, Intestinal Methanogen Overgrowth (IMO), and Small Intestinal Fungal Overgrowth (SIFO) in IBS pathogenesis, focusing on prevalence, mechanisms, and targeted therapy. Material and methods. A literature review was performed using PubMed and Scopus (2000 - 2025). The analysis included 45 sources, including meta-analyses, systematic reviews, and clinical guidelines (Rome IV, Polish Society of Gastroenterology). Results. Meta-analyses indicate that IBS patients are nearly five times more likely to test positive for SIBO than healthy individuals (OR 4.7). Hydrogen-producing bacteria are linked to diarrhea (IBS-D), while methane delays transit, correlating with constipation (IBS-C). Proposed mechanisms include excessive fermentation gas, bile acid deconjugation, and increased intestinal permeability. SIFO is found in 25% of refractory cases. Targeted eradication particularly with rifaximin achieves symptom resolution, with 48% of treated patients no longer meeting Rome criteria. However, diagnostic inconsistencies in breath tests remain a subject of clinical controversy. Conclusions. SIBO and IMO represent treatable pathomechanisms in a subset of IBS patients, supporting a transition to personalized, mechanism-based management. Identifying these phenotypes is essential for optimizing targeted antimicrobial and prokinetic therapy. Individualized diagnostics are crucial for managing the micro-organic subtype of this complex syndrome.