Small Intestinal Bacterial Overgrowth in Irritable Bowel Syndrome: Frequency and Microbiological Insights from Duodenal Aspirate Analysis

Author(s): Mohammad Jane Alam, M Masudur Rahman, Subrata Poddar Chayan, Sadia Sultana Kamolika, Nasreen Farhana

Background: Small Intestinal Bacterial Overgrowth (SIBO) has been implicated in the pathophysiology of Irritable Bowel Syndrome (IBS), particularly in diarrhea-predominant (IBS-D) and mixed-type (IBS-M) subtypes. This study aimed to determine the frequency of SIBO and analyze the microbiological profile of duodenal aspirate cultures in IBS patients.

Methods: This observational cross-sectional study conducted at department of Gastroenterology, Dhaka medical college hospital, Dhaka; from September 2018 to August 2019 and included 104 IBS patients diagnosed based on Rome IV criteria. Duodenal aspirate samples were collected and cultured, with SIBO defined as ≥10⁵ CFU/mL of bacterial growth. The frequency of SIBO was compared between IBS subtypes, and the isolated bacterial species were identified.

Results: SIBO was detected in 38 (36.5%) of IBS patients, with a higher prevalence in IBS-D (53.3%) compared to IBS-M (13.7%). Culture positivity was observed in 60.6% of cases. Pseudomonas (78.9%) was the most frequently isolated organism in SIBO-positive patients, followed by E. coli (21.1%). In contrast, Klebsiella and Citrobacter were only found in SIBO-negative cases.

Conclusion: SIBO was significantly associated with IBS-D, suggesting a potential pathogenic role of Pseudomonas and E. coli in symptom development. The findings emphasize the importance of screening for SIBO in IBS-D patients for targeted therapeutic interventions. Further large-scale studies are needed to validate these observations.