Mucus Brushing and SIBO: Frontline Gastroenterology, March 2026

Introduction

Upper small intestinal bacterial overgrowth (USIBO) is characterised by excessive bacterial colonisation in the duodenum or proximal jejunum, often leading to symptoms such as bloating, abdominal distension, and dyspepsia. Diagnosing USIBO remains challenging. Current methods include breath tests (glucose or lactulose hydrogen testing) and duodenal fluid aspiration, but both have important limitations. Breath tests have variable sensitivity and specificity, while aspirate cultures can be difficult to obtain and are prone to contamination and dilution, resulting in false-positive rates of up to 20%. These challenges have prompted exploration of alternative diagnostic techniques.

Summary

This study revisits the duodenal mucus brushing technique, an older but largely overlooked method for detecting bacterial overgrowth. During endoscopy, a cytology brush is used to collect mucus directly from the duodenal or proximal jejunal mucosa, targeting bacteria adherent to the mucosal surface rather than bacteria suspended in luminal fluid.

In a cohort of 92 patients with suspected USIBO, bacterial growth was detected in 24% of cases using this technique. Streptococcus species were the most commonly identified organisms, followed by coliform bacteria. Importantly, contamination testing demonstrated a false-positive rate of only 8%, significantly lower than that reported with traditional duodenal aspiration.

The authors propose that bacteria involved in USIBO preferentially adhere to the mucosal mucus layer, making mucus sampling a more accurate diagnostic source. The brushing technique is simple, reproducible, and can be performed during routine endoscopy, potentially improving the detection of small intestinal bacterial overgrowth in patients lacking duodenal fluid samples.