Introduction
Irritable bowel syndrome (IBS) is a prevalent functional gastrointestinal disorder characterized by abdominal pain and changes in bowel habits. Small intestinal bacterial overgrowth (SIBO) refers to a group of gastrointestinal syndromes caused by an excessive number of bacteria in the small intestine. Up to now, the relationship between IBS and SIBO remains contentious. So we set out to investigate the differences between these two conditions.
Aims & Methods
Participants who met the Rome III diagnostic criteria for IBS and had a negative lactulose hydrogen and methane breath test (LHMBT) were diagnosed with IBS. Those who presented with gastrointestinal symptoms and had a positive LHMBT were diagnosed with SIBO. Overlapping cases were excluded. Participants who had a negative LHMBT and no significant abdominal symptoms were classified as healthy controls (HC). All participants were instructed to provide fecal samples for 16S rRNA sequencing.
Results
Our results showed that a history of enteritis was more common in IBS patients, and the severity of gastrointestinal symptoms was significantly higher in IBS and SIBO groups compared to healthy controls. IBS patients also reported more severe symptoms than SIBO. Additionally, IBS patients were more affected by their symptoms, while the SIBO group reported more dissatisfaction with bowel habits. We observed differences in dietary intake between the groups, with IBS patients having the highest total energy and protein intake, and the lowest dietary fiber intake. SIBO patients had higher fat intake and significantly lower carbohydrate intake compared to the other two groups. Regarding the fecal microbiome, both IBS and SIBO patients had higher structural diversity and lower functional diversity than the HC group. The abundance of Firmicutes/Bacteroidetes in the IBS group was significantly higher than in the other two groups. Our analyses indicated that the fecal microbiome could significantly distinguish the three groups, and specific bacterial species were associated with different symptoms in each group. In SIBO, Thalassospira and Christensenellaceae_group were associated with intestinal motility abnormalities, while Ruminococcaceae_group, Butyricimonas, and Oscillospira were associated with gas production. In the IBS group, Klebsiella and Mitsuokella were associated with abdominal pain, and other bacteria such as Escherichia_Shigella and Enterobacter were generally associated with enteritis infection, abdominal pain, and diarrhea. We also found that the predicted KEGG pathways were enriched in various nutrient metabolism pathways, with potential implications for elevated blood folate levels and vitamin B12 deficiency in SIBO patients.Protein bacterial motility and biofilm formation_ Escherichia coli, were mainly enhanced in IBS, and these functions were related to the mucosal barrier damage.
Conclusion
Our study shows that although IBS and SIBO share similar symptom spectra, they may be two distinct diseases. Despite the potential differences in the fecal flora of small intestinal flora in SIBO group, significant differences were found between IBS and SIBO in terms of clinical phenotype and fecal microbiome. Further exclusion of SIBO using lactulose hydrogen and methane breath testing in patients who meet the diagnostic criteria for IBS is warranted, as the differences suggest that different treatment strategies may be needed for these two populations. Future studies are needed to explore the underlying mechanisms and potential therapies for these conditions, which may ultimately benefit patients with IBS and SIBO.
References
1. Quigley EMM, Murray JA, Pimentel M. AGA Clinical Practice Update on Small Intestinal Bacterial Overgrowth: Expert Review. Gastroenterology. 2020; 159(4):1526-1532. DOI: 10.1053/j.gastro.2020.06.090
2. Bushyhead D, Quigley EMM. Small Intestinal Bacterial Overgrowth-Pathophysiology and Its Implications for Definition and Management. Gastroenterology. 2022; 163(3):593-607. DOI: 10.1053/j.gastro.2022.04.002
3. Ghoshal UC, Nehra A, Mathur A, Rai S. A meta-analysis on small intestinal bacterial overgrowth in patients with different subtypes of irritable bowel syndrome. J Gastroenterol Hepatol. 2020; 35(6):922-931. DOI: 10.1111/jgh.14938
4. Mearin F,Lacy BE,Chang L, et al. BowelDisorders[J].Gastroenterology,2016;150;1393-1407.
5. Zhu L, Huang D, Shi L, et al.Intestinal symptoms and psychological factors jointly affect quality of life of patients with irritable bowel syndrome with diarrhea.Health
Qual Life Outcomes. 2015;13:49.
6. Sperber AD,Dumitrascu D, Fukudo S, et al.Gut 2017;66:1075–1082
7. Jindong Zhang, Jiao Liu, Shiwei Zhu, Ben Wang, Qiong Jia, Qihua He, Lijin Song, Yuan Fang, Baoli Zhu, Liping Duan. Berberine alleviates visceral hypersensitivity in rats by altering gut microbiome and suppressing spinal microglial activation. Acta Pharmacologica Sinica，Accepted 2020
