Altered Colonic Bacterial Fermentation as a Potential Pathophysiological Factor in Irritable Bowel Syndrome

Abstract

OBJECTIVES Dysbiosis leading to abnormal intestinal fermentation has been suggested as a possible etiological mechanism in irritable bowel syndrome (IBS). We aimed to investigate the location and magnitude of altered intestinal bacterial fermentation in IBS and its clinical subtypes. METHODS One hundred fourteen IBS patients who satisfied Rome III criteria and 33 healthy controls (HC) were investigated. Intestinal fermentation was assessed using two surrogate measures: intestinal intraluminal pH and fecal short chain fatty acids (SCFAs). Intraluminal pH and intestinal transit time were measured in the small and large bowel using a wireless motility capsule (SmartPill™) in 47 IBS and 10 HC. Fecal SCFAs including acetate, propionate, butyrate and lactate were analyzed by capillary gas chromatography in all enrolled subjects. Correlations between intestinal pH, fecal SCFAs, intestinal transit time and IBS symptom scores were analyzed. RESULTS Colonic intraluminal pH levels were significantly lower in IBS patients compared to HC (total colonic pH, 6.8 for IBS vs. 7.3 for HC, P = 0.042). There were no differences in total and segmental pH levels in the small bowel between IBS patients and HC (6.8 vs. 6.8, P = NS). The intraluminal colonic pH differences were consistent in all IBS subtypes. Total SCFAs level was significantly lower in C-IBS patients than in D-IBS and M-IBS patients and HC. The total SCFAs level in all IBS subjects was similar with that of HC. Colonic pH levels correlated positively with colon transit time (CTT) and IBS symptoms severity. Total fecal SCFAs levels correlated negatively with CTT, and positively with stool frequency. CONCLUSIONS Colonic intraluminal pH is decreased, suggesting higher colonic fermentation, in IBS patients compared with HC. Fecal SCFAs are not a sensitive marker to estimate intraluminal bacterial fermentation.

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“…The pH of each fecal sample was assessed by inserting an electrode pH probe (pHSpear; Eutech Instruments, Thermo Fisher Scientific) into 3 different locations of each stool. With the use of sterile spatulas, small pieces of the stools were removed and immediately frozen in liquid nitrogen for later analysis of SCFA content (acetate, propionate, butyrate, isobutyrate, valerate, and isovalerate) with the use of a Hewlett-Packard model 6890 gas chromatograph with a flame ionization detector equipped with a 30 m, 0.53 mm ID capillary column, as previously described (18,19). Remaining fecal samples were weighed, and twice this weight in ultra-pure (Milli-Q) sterile water was added to each sample.…”

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“…Following assessment of starch fermentation in vitro, the microbiota of IBS patients produced more sulfides and hydrogen, and less butyrate, than those of healthy controls. Another study assessed intestinal fermentation in 114 patients with Rome III-defined IBS and 33 healthy controls, using intraluminal pH measured via wireless motility capsule, and levels of short-chain fatty acids in stool [47]. Colonic, but not small bowel, pH was significantly lower among IBS patients compared with controls, suggesting higher levels of colonic fermentation in IBS.…”