168. Intestinal Motility and Overlap Among Intestinal Methanogen Overgrowth (IMO), Hydrogen-Dominant Small Intestinal Bacterial Overgrowth, and Hydrogen Sulfide-Dominant SIBO

In this episode, we detail the pathophysiology of intestinal methanogen overgrowth (IMO), hydrogen-dominant small intestinal bacterial overgrowth (H₂-SIBO), and hydrogen sulfide-dominant SIBO (H₂S-SIBO), discussing their mechanistic interactions and overlap. We discuss methanogenic archaea, as well hydrogen sulfide- and hydrogen-producing microbes and their contributions to altered gastrointestinal motility, epithelial barrier function, and neuromuscular signaling. We detail host endogenous defense mechanisms, including gastric acid secretion, pancreatic enzymatic activity, bile flow, intestinal motility, and more.

Topics:

1. Introduction

- Overview of intestinal methanogen overgrowth (IMO), hydrogen sulfide-dominant SIBO, and hydrogen-dominant SIBO 

- Discussion of overlap

2. Intestinal Methanogen Overgrowth (IMO)

- Characterized by an overabundance of methane-producing archaea 

- Methane and intestinal transit

- Bloating, abdominal discomfort, constipation 

- Associated with irritable bowel syndrome with constipation (IBS-C) 

3. Overlap Between IMO and SIBO Subtypes

- Hydrogen as a substrate for methane and/or hydrogen sulfide production

- Shared potential root causes

4. Small Intestinal Bacterial Overgrowth (SIBO) and Protective Mechanisms

- The small intestine remains relatively free of bacteria due to protective mechanisms 

- Gastric acid secretion 

- Pancreatic enzymes and bile

- Intestinal motility

- Structural abnormalities

5. Hydrogen-Dominant SIBO

- Increased hydrogen and intestinal transit

- Potential symptoms, diarrhea, postprandial bloating 

- Different forms of SIBO can coexist

6. Hydrogen Sulfide-Dominant SIBO

- H₂S and intestinal motility

- H₂S and intestinal epithelial integrity

- Symptoms, associations with IBS diarrhea   

7. Host Defense Mechanisms Regulating Microbial Balance

- Gastric acid secretion, pancreatic enzyme activity, bile flow, intestinal motility, and more

8. Gastric Acid and Its Role in Microbial Regulation

- Parietal cells secrete hydrochloric acid (HCl) and intrinsic factor 

- Chief cells secrete pepsinogen, conversion into pepsin in acidic conditions 

- Gastric acid, digestion and antimicrobial defense 

9. Hypochlorhydria

- Low gastric acid impairs microbial defense

- Reduced acidity disrupts digestion and downstream pancreatic enzyme and bile release 

10. Pancreatic Enzymes and Their Role in Microbial Regulation

- Pancreatic enzymes, digestion, antimicrobial activity

- Enzymes modify chyme to limit fermentable substrates that fuel microbial proliferation 

11. Intestinal Motility

- Coordinated contractions propel food, microbes, and waste through the GI tract 

- The enteric nervous system (ENS) and gut motility

- The myenteric plexus controls peristalsis, while the submucosal plexus regulates secretion and absorption 

12. Conclusion

- Intestinal methanogen overgrowth (IMO), hydrogen-dominant SIBO, and hydrogen sulfide-dominant SIBO 

- Overlap in symptoms and microbial interactions 

- Host defense mechanisms, including gastric acid, pancreatic enzymes, and motility 

- Intestinal motility and ENS function in microbial homeostasis 

- Hydrogen sulfide as a gasotransmitter

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