Bacterial Dysbiosis Due to Hydrogen Sulfide-Producing Gut Bacteria – SIBO
Content
1. What is SIBO?
1.1 SIBO Testing and Diagnosis
1.2 Treatment Approaches for SIBO
2. Types of SIBO
2.1 Hydrogen – Dominant SIBO
2.2 Methane – Dominant SIBO (IMO)
2.3 Hydrogen Sulfide SIBO
3. Diagnosis of Hydrogen Sulfide SIBO
4. Effects of Hydrogen Sulfide on the Gut
5. Brain Fog and the Gut-Brain Axis
6. What to Do if You Have Hydrogen Sulfide SIBO
1. What is SIBO?
SIBO, or Small Intestinal Bacterial Overgrowth, is a digestive condition characterized by an elevated and pathological overgrowth of bacteria in the small intestine. In contrast to the large intestine, a healthy gut contains only minimal bacteria in the small bowel. However, when bacterial dysbiosis occurs in this region, it can lead to negative effects on digestion and nutrient absorption.
In these cases, excessive bacteria begin to produce gas and toxins, overwhelming the gut. The result is a range of symptoms, including abdominal pain, bloating, gas, flatulence, diarrhea, constipation, belching, early satiety, and acid reflux. These issues often overlap with conditions like IBS (Irritable Bowel Syndrome), making accurate diagnosis crucial.
1.1 SIBO Testing and Diagnosis
SIBO can be diagnosed using a non-invasive breath test. This testing involves consuming test sugars like lactulose, glucose, lactose, or fructose (1)—each offering different approaches and sensitivity depending on the dominant microbial activity. Bacteria ferment these sugars and produce gases such as hydrogen or methane, which are then exhaled and measured.
If elevated levels of hydrogen or methane are detected in the breath, it indicates contact with bacterial overgrowth in the small intestine. Human cells do not produce these gases, so their presence is a positive indicator of microbial activity.
1.2 Treatment Approaches for SIBO
Once diagnosed, various approaches to treatment are available. These include a targeted SIBO diet, herbal or conventional antibiotics (2), and probiotics. The most effective method depends on the dominant bacteria, patient symptoms, and whether the condition is acute or chronic. For best results, treatment should be guided by a healthcare provider experienced with gut conditions like IBS or IMO (Intestinal Methanogen Overgrowth).
2. Types of SIBO
SIBO is classified based on the gas that is predominantly produced: hydrogen (H₂), methane (CH₄), or hydrogen sulfide (H₂S). Each type has unique symptoms and treatment approaches.
2.1 Hydrogen Dominant SIBO
Hydrogen SIBO is caused by bacteria like E. coli and Klebsiella, which produce hydrogen gas during fermentation. Common symptoms include diarrhea, bloating, and excessive gas. This form is often found in patients with IBS-like conditions.
2.2 Methane – Dominant SIBO (IMO)
When methane is the dominant gas, the condition is more accurately referred to as IMO – Intestinal Methanogen Overgrowth. Methane is produced by archaea, not bacteria, and is commonly associated with constipation. IMO is considered a subtype of SIBO, with distinct issues and requires tailored treatment (3).
2.3 Hydrogen Sulfide SIBO
This lesser-known form involves hydrogen sulfide–producing bacteria such as Escherichia coli. Symptoms include diarrhea (5), constipation (6), bloating, and gas with a rotten-egg smell. Patients may also report brain fog, a negative cognitive state marked by poor concentration and memory.
3. Diagnosis of Hydrogen Sulfide SIBO
Hydrogen sulfide SIBO is harder to detect, as no breath test in Germany currently measures H₂S directly. Instead, diagnosis relies on symptoms and indirect breath test indicators using lactulose. If after 180 minutes no significant gas increase is seen, it may suggest early breakdown by hydrogen sulfide–producing bacteria—evidence of contact with SIBO in the small intestine:
Since lactulose can only be metabolized by bacteria, a significant increase in the measured gases should be observed around 120 minutes into the evaluation. After roughly two hours, the lactulose solution typically reaches the large intestine, where it is broken down by the naturally occurring bacteria. If this increase is still not seen after 180 minutes of testing, it suggests that the solution was already broken down earlier—by hydrogen sulfide–producing bacteria in the small intestine.
4. Effects of Hydrogen Sulfide on the Gut
Hydrogen sulfide is a gasotransmitter (7), involved in both positive and negative processes. It regulates gut motility, hormone secretion, and inflammation (7). In elevated concentrations, however, it can harm the gut lining and contribute to systemic issues. Understanding its dual role is essential for developing effective diet and treatment approaches (7).
5. Brain Fog and the Gut-Brain Axis
Brain fog, frequently seen in hydrogen sulfide SIBO, refers to a state of cognitive cloudiness or disorientation. Although the exact mechanism is unclear, the gut-brain axis likely plays a role. This connection highlights the need for a comprehensive strategy that addresses both digestive and neurological symptoms in affected patients.
6. What to Do if You Suspect Hydrogen Sulfide SIBO
If you are experiencing symptoms such as persistent bloating, abdominal pain, gas, or brain fog, speak with a healthcare provider about appropriate testing. Evidence-based approaches include breath tests, tailored diets, probiotics, and antimicrobial treatments. Eliminating trigger foods, supporting a healthy gut microbiome, and addressing root causes are essential for long-term recovery.
References
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- Ginnebaugh B, Chey WD, Saad R. Small Intestinal Bacterial Overgrowth: How to Diagnose and Treat (and Then Treat Again). Gastroenterol Clin North Am. 2020 Sep;49(3):571-587. doi: 10.1016/j.gtc.2020.04.010. Epub 2020 Jun 14. PMID: 32718571.
- Takakura W, Pimentel M. Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome – An Update. Front Psychiatry. 2020 Jul 10;11:664. doi: 10.3389/fpsyt.2020.00664. PMID: 32754068; PMCID: PMC7366247.
- Takakura W, Pimentel M. Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome – An Update. Front Psychiatry. 2020 Jul 10;11:664. doi: 10.3389/fpsyt.2020.00664. PMID: 32754068; PMCID: PMC7366247.
- Pimentel M, Hosseini A, Chang C, Mathur R, Rashid M, Sedighi R, et al. Fr248 EXHALED HYDROGEN SULFIDE IS INCREASED IN PATIENTS WITH DIARRHEA: RESULTS OF A NOVEL COLLECTION AND BREATH TESTING DEVICE. Gastroenterology. 2021 May;160(6):S-278. DOI: 10.1016/S0016-5085(21)01391-3.
- Guo HZ, Dong WX, Zhang X, Zhu SW, Liu ZJ, Duan LP. [The diagnostic value of hydrogen sulfide breath test for small intestinal bacterial overgrowth]. Zhonghua Nei Ke Za Zhi. 2021 Apr 1;60(4):356-361. Chinese. doi: 10.3760/cma.j.cn112138-20200731-00725. PMID: 33765706.
- Singh SB, Lin HC. Hydrogen Sulfide in Physiology and Diseases of the Digestive Tract. Microorganisms. 2015 Nov 12;3(4):866-89. doi: 10.3390/microorganisms3040866. PMID: 27682122; PMCID: PMC5023273.
