Background The profile of intestinal organic acids in irritable bowel syndrome (IBS) and its correlation with gastrointestinal (GI) symptoms are not clear. We hypothesized in this study that altered GI microbiota contribute to IBS symptoms through increased levels of organic acids. Methods Subjects were 26 IBS patients and 26 age- and sex-matched controls. Fecal samples were collected for microbiota analysis using quantitative real-time polymerase chain reaction and culture methods, and the determination of organic acid levels using high-performance liquid chromatography. Abdominal gas was quantified by image analyses of abdominal X-ray films. Subjects completed a questionnaire for GI symptoms, quality of life (QOL) and negative emotion. Key Results Irritable bowel syndrome patients showed significantly higher counts of Veillonella (P = 0.046) and Lactobacillus (P = 0.031) than controls. They also expressed significantly higher levels of acetic acid (P = 0.049), propionic acid (P = 0.025) and total organic acids (P = 0.014) than controls. The quantity of bowel gas was not significantly different between controls and IBS patients. Finally, IBS patients with high acetic acid or propionic acid levels presented with significantly worse GI symptoms, QOL and negative emotions than those with low acetic acid or propionic acid levels or controls. Conclusions & Inferences These results support the hypothesis that both fecal microbiota and organic acids are altered in IBS patients. A combination of Veillonella and Lactobacillus is known to produce acetic and propionic acid. High levels of acetic and propionic acid may associate with abdominal symptoms, impaired QOL and negative emotions in IBS.
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