Methanobrevibacter smithii Is the Predominant Methanogen in Patients with Constipation-Predominant IBS and Methane on Breath
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Among irritable bowel syndrome (IBS) patients, breath methane producers overwhelmingly have constipation predominance (C-IBS). Although the most common methanogen in humans is Methanobrevibacter smithii, incidence and type of methanogenic bacteria in C-IBS patients are unknown.
By use of a questionnaire and lactulose breath testing, subjects with Rome II C-IBS and methane (>3 ppm) were selected (n = 9). The control group included subjects with IBS who had no breath methane (n = 10). Presence of bacterial DNA was assessed in a stool sample of each subject by quantitative-PCR using universal 16S rDNA primer. M. smithii was quantified by use of a specific rpoB gene primer.
M. smithii was detected in both methane and non-methane subjects. However, counts and relative proportion of M. smithii were significantly higher for methane-positive than for methane-negative subjects (1.8 × 107 ± 3.0 × 107 vs 3.2 × 105 ± 7.6 × 105 copies/g wet stool, P < 0.001; and 7.1 ± 6.3 % vs 0.24 ± 0.47 %, P = 0.02 respectively). The minimum threshold of M. smithii resulting in positive lactulose breath testing for methane was 4.2 × 105 copies/g wet stool or 1.2 % of total stool bacteria. Finally, area-under-curve for breath methane correlated significantly with both absolute quantity and percentage of M. smithii in stool (R = 0.76; P < 0.001 and R = 0.77; P < 0.001 respectively).
M. smithii is the predominant methanogen in C-IBS patients with methane on breath testing. The number and proportion of M. smithii in stool correlate well with amount of breath methane.
KeywordsConstipation IBS Methane Methanogens
We would like to thank the Beatrice and Samuel A. Seaver Foundation for their ongoing support of our research in the GI Motility Program at Cedars-Sinai Medical Center.
Conflict of interest
Dr Mark Pimentel is a consultant for and has grants from Salix Pharmaceuticals. Cedars-Sinai has a licensing agreement with Salix Pharmaceuticals. All other authors have no financial conflicts to disclose.
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