Small intestinal bacterial overgrowth is associated with irritable bowel syndrome and is independent of proton pump inhibitor usage.

BACKGROUND: Current knowledge suggests that small intestinal overgrowth participates in the pathogenesis of irritable bowel syndrome. It is questionable if this association is modulated by intake of proton pump inhibitors (PPIs). METHODS: In a prospective study, quantitative cultures of duodenal aspirates were performed for aerobic species in 897 consecutive patients undergoing upper GI tract endoscopy. SIBO was defined as equal to or more than 10(3) cfu/ml. The effect of PPI intake on the relationship between SIBO and IBS was the primary endpoint. RESULTS: Analysis among patients without any history of PPI intake (n = 713) showed that odds ratio (OR) for IBS in the event of SIBO was 5.63 (3.73-8.51, p < 0.0001); this was 4.16 (1.91-9.06) when analysis was done among patients with history of PPI intake (n = 184, p: 0.498 between patients without and with PPI intake). Multiple logistic regression analysis found that factors independently associated with SIBO were age above or equal to 60 years (OR: 2.36), body mass index more than or equal to 22 kg/m(2) (OR: 0.60), presence of IBS (OR: 6.29), type 2 diabetes mellitus (OR: 1.59) and gastritis (OR: 0.47). CONCLUSIONS: The association between IBS and SIBO was completely independent from PPI intake. Although gastritis was protective against SIBO, results show that PPI intake cannot prime SIBO.

Small Intestine Bacterial Overgrowth Can Form an Indigenous Proinflammatory Environment in the Duodenum: A Prospective Study.

Small intestinal bacterial overgrowth (SIBO) contributes to the formation of an inflammatory environment in various intestinal and extraintestinal diseases. Cytokines that participate in these mechanisms are yet to be examined. Upper gastrointestinal endoscopy with duodenal aspiration was performed in 224 patients. Quantitative cultures of aerobic species were performed, concentrations of interleukin 1ß (IL-1ß), interleukin 6 (IL-6), and tumor necrosis factor alpha (TNF-α) were measured, and loads of Escherichia coli, Klebsiella pneumoniae, Methanobevibacter smithii, and Aeromonas spp. were detected via real-time PCR in the duodenal fluid. Analysis showed that the odds ratio (OR) for elevated IL-1ß levels was 2.61 (1.06-6.43, p = 0.037) among patients with SIBO compared to patients without SIBO, while there was no significant difference at elevated IL-6 and TNF-α levels between patients with and without SIBO, using ≥10³ cfu/mL as a cut-off. The presence of all three elevated cytokine levels has OR 3.47 (1.06-11.34, p = 0.030) among patients with SIBO. Klebsiella pneumoniae detection was positively related with IL-6 and TNF-α levels, when Methanobevibacter smithii was positively related with IL-1ß levels. The presence of SIBO is associated with elevated IL-1ß levels in the duodenal fluid. There is a high prevalence of all three proinflammatory cytokine levels elevated (IL-1ß, IL-6, and TNF-α) in the duodenal fluid among patients with SIBO.

In vitro activity of rifaximin against isolates from patients with small intestinal bacterial overgrowth.

Rifaximin, a non-absorbable rifamycin derivative, has published clinical efficacy in the alleviation of symptoms in patients with irritable bowel syndrome (IBS). Small intestinal bacterial overgrowth (SIBO) is associated with the pathogenesis of IBS. This study describes for the first time the antimicrobial effect of rifaximin against SIBO micro-organisms from humans. Fluid was aspirated from the third part of the duodenum from 567 consecutive patients; quantitative cultures diagnosed SIBO in 117 patients (20.6%). A total of 170 aerobic micro-organisms were isolated and the in vitro efficacy of rifaximin was studied by (i) minimum inhibitory concentration (MIC) testing by a microdilution technique and (ii) time-kill assays using bile to simulate the small intestinal environment. At a breakpoint of 32 µg/mL, rifaximin inhibited in vitro 85.4% of Escherichia coli, 43.6% of Klebsiella spp., 34.8% of Enterobacter spp., 54.5% of other Enterobacteriaceae spp., 82.6% of non-Enterobacteriaceae Gram-negative spp., 100% of Enterococcus faecalis, 100% of Enterococcus faecium and 100% of Staphylococcus aureus. For the time-kill assays, 11 E. coli, 15 non-E. coli Gram-negative enterobacteria and three E. faecalis isolates were studied. Rifaximin produced a >3 log10 decrease in the starting inoculum against most of the tested isolates at 500 µg/mL after 24h of growth. The results indicate that rifaximin has a potent effect on specific small bowel flora associated with SIBO. This conclusion should be regarded in light of the considerable time-kill effect at concentrations lower than those achieved in the bowel lumen after administration of conventional doses in humans.