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SIBO AND ITS VARIATIONS

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There are three variations of bacterial overgrowth: SIBO, IMO, and excess hydrogen sulfide.

SIBO

Small intestinal bacterial overgrowth, or SIBO, is defined as the presence of excessive numbers of bacteria in the small bowel, causing frustrating and often painful gastrointestinal symptoms. The small intestine usually has lower levels of bacteria than the colon. When there is an overgrowth of bacteria in the small intestine, the normal balance in the gut microbiome is significantly disrupted, causing the symptoms of SIBO.

 

To treat the overgrowth of bacteria in a patient, first a healthcare provider will usually prescribe a breath test. This will allow the provider to determine the root cause of the patient’s symptoms. 

 

A breath test measures fermented gases in the breath of patients experiencing gastrointestinal symptoms. The three primary fermented gases are hydrogen, methane, and hydrogen sulfide. Each gas is associated with a particular condition. To determine if a patient is experiencing SIBO, the provider will look closely at the levels of hydrogen in a patient’s breath. 

 

Once SIBO is formally ruled in with the aid of a breath test, effective treatments like antibiotics and diet modification can be prescribed. In some cases, corrective surgeries are also available to help with managing SIBO symptoms.

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SIBO SYMPTOMS

Patients with SIBO often experience the following symptoms once a week or more for at least four weeks: 

 

  • Bloating

  • Distension

  • Abdominal pain

  • Gas 

  • Flatulence

  • Diarrhea

  • Constipation

 

These symptoms can masquerade as other illnesses. The symptom most commonly reported by patients with SIBO is bloating, often after eating. 

 

WHAT CAUSES SIBO?

SIBO can be a complex result of various medications and conditions. Patients with irritable bowel syndrome (IBS) and suspected motility disorders are at high risk for developing SIBO. Many people don’t know that up to 80% of IBS patients could also have SIBO.  

 

Other at risk patients may have experienced:

 

  • Structural damage, injury, or defects in the small intestine

  • Diabetes

  • Radiation therapy

  • Diverticulosis

  • Intestinal lymphoma

  • Crohn's disease 

  • Scleroderma

  • Gastric surgery (obesity or ulcers)

  • Fistula 

 

Certain surgeries are often responsible for SIBO because food and waste can linger in the intestines due to impaired motility as a result of particular surgical procedures. In these cases, because there is now more food and waste available to the bacteria in the gut to feed on, the bacteria colonize and multiply, resulting in bacterial overgrowth. 

 

WHICH GAS INDICATES SIBO?

Excess levels of hydrogen are produced when certain bacteria consume food in the small bowel. Elevated levels of hydrogen, as measured by a breath test, are indicative of SIBO. 

IMO

Intestinal methanogenic overgrowth, or IMO, is an overgrowth of methane-producing archaea in the small and large intestines.  This condition was previously called “methane SIBO,” however; that term isn’t quite accurate. Methanogens are not bacteria (the “B” in SIBO) but are archaea, a group of single-celled organisms lacking a defined nucleus. These methanogens may also overgrow in the colon and not just the small intestine (the “SI” in SIBO).  

 

IMO SYMPTOMS

Patients with IMO experience symptoms similar to SIBO: abdominal pain, bloating, gas, distension, flatulence, but especially constipation.  The level of methane measured by a breath test correlates with the severity of constipation. These symptoms are usually experienced once a week or more for at least four weeks. IMO also shares many symptoms with IBS-C (constipation-predominant irritable bowel syndrome) and IBS-M (mixed-diarrhea/constipation irritable bowel syndrome). 

 

WHAT CAUSES IMO?

The causes of IMO overlap with the causes of SIBO and include medications and other GI conditions. More research is being done to determine the distinct causes of IMO. 

 

WHICH GAS INDICATES IMO?

Methane is produced when archaea consume hydrogen. Elevated levels of methane, as measured by a breath test, are indicative of IMO. A positive methane breath test is associated with constipation, and the level of methane measured correlates with the severity of constipation. 

EXCESS HYDROGEN SULFIDE 

Excess hydrogen sulfide is a condition that is the result of the overgrowth of hydrogen sulfide-producing organisms. Measuring hydrogen sulfide to determine excess overgrowth was previously not possible until recent technological breakthroughs in breath testing. trio-smart is the only three-gas breath test available that measures hydrogen, methane, and, for the first time, hydrogen sulfide. Patients with elevated hydrogen sulfide often went unrecognized on previous one-gas or two-gas breath tests.

 

EXCESS HYDROGEN SULFIDE SYMPTOMS

Patients with excess hydrogen sulfide share common symptoms with SIBO: abdominal pain, bloating, gas, distension, flatulence, but especially diarrhea. Levels of hydrogen sulfide, as measured by a breath test, correlate with the severity of diarrhea. These symptoms are usually experienced once a week or more for at least four weeks. Excess hydrogen sulfide shares many of the symptoms of IBS-D (diarrhea-predominant irritable bowel syndrome) and IBS-M (mixed-diarrhea/constipation irritable bowel syndrome). 

 

WHAT CAUSES EXCESS HYDROGEN SULFIDE?

Excess hydrogen sulfide is caused when organisms in the gut consume hydrogen and produce hydrogen sulfide. Because the ability to capture and measure hydrogen sulfide is so new, additional research is being done to determine the root cause of excess hydrogen sulfide and the treatments for those suffering from this condition. 

 

WHICH GAS INDICATES EXCESS HYDROGEN SULFIDE?

Hydrogen sulfide is produced when hydrogen sulfide-producing organisms consume hydrogen. Elevated levels of hydrogen sulfide, as measured by a breath test, are indicative of excess hydrogen sulfide. A positive hydrogen sulfide breath test predicts more severe diarrhea, and the level of hydrogen sulfide measured correlates with the severity of diarrhea. 

BREATH TESTING

Breath testing is a way for healthcare providers to identify certain conditions related to the gut microbiome by analyzing fermented gases found in patients’ exhaled breath. There are three fermented gases detectable with breath testing:  hydrogen, methane, and newly measurable hydrogen sulfide. While healthy levels of hydrogen, methane, and hydrogen sulfide can be present in the gut microbiome, abnormal levels can indicate a disorder and provide valuable insight into the proper treatment.

 

HYDROGEN, METHANE, AND HYDROGEN SULFIDE DO NOT ACT INDEPENDENTLY.

Hydrogen, methane, and hydrogen sulfide interact with each other in a complex way. Hydrogen is produced by fermenting bacteria but is also consumed by other organisms, resulting in the production of other gases, including methane and hydrogen sulfide. 

 

There is a balance-counterbalance effect between methane and hydrogen sulfide, illustrating a biochemical interdependency between microbes in the microbiome. These findings are important, because they indicate limitations when measuring only one or two of the three primary fermented gases. 

 

THREE-GAS BREATH TESTING

Prior to the breakthrough three-gas breath testing technology of trio-smart, testing for bacterial overgrowth was limited to the measurement of only two of the three primary fermented gases: hydrogen and methane. 

 

Hydrogen sulfide is important to measure, because it is the only gas strongly associated with more severe diarrhea, with the level of hydrogen sulfide correlating with the severity of diarrhea. Hydrogen sulfide was previously undetectable, so patients with elevated hydrogen sulfide often went unrecognized by one-gas or two-gas breath tests. 

 

Measuring hydrogen and methane can offer a partial story about a patient’s GI symptoms. With a three-gas breath test, all three primary fermented  gases in the microbiome - hydrogen, methane, and hydrogen sulfide - can be measured, offering the most complete picture. 

REFERENCES

 

Pimentel, M., Saad, R., Long, M., & Rao, S. ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. The American Journal of Gastroenterology, 2020.

 

Rezaie, A., Buresi, M., Lembo, A., Lin, H., McCallum, R., Rao, S., Schmulson, M., Valdovinos, M., Zakko, S., & Pimentel, M. Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus. American Journal of Gastroenterology, 2017. 

 

Lacy, B., Pimentel, M., Brenner, D., Chey, W., Keefer, L., Long, M., & Moshiree, B. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. The American Journal of Gastroenterology, 2021.

 

Pimentel, M., Hosseini, A., Chang, C., Mathur, R., Rashid, M., Sedighi, R., Fowler, H., Torosyan, J., Wang, J., & Rezaie, A. Exhaled Hydrogen Sulfide Is Increased in Patients With Diarrhea: Results of a Novel Collection and Breath Testing Device. AGA Abstracts, 2021. 

 

Singer-Englar, T., Rezaie, A., Gupta, K., Pichetshote, N., Sedighi, R., Lin, E., Chua, K., & Pimentel, M. Competitive Hydrogen Gas Utilization by Methane- and Hydrogen Sulfide-Producing Microorganisms and Associated Symptoms: Results of a Novel 4-Gas Breath Test Machine. AGA Abstracts, 2021.

 

Pimentel, M., Mathur, R., & Chang, C. Gas and the Microbiome. Current Gastroenterology, 2013.


Singer-Englar, T., Rezaie, A., Gupta, K., Pichetshote, N., Sedighi, R., Lin, E., Chua, K., & Pimentel, M. Validation of a 4-Gas Device for Breath Testing in the Determination of Small Intestinal Bacterial Overgrowth. AGA Abstracts, 2018.

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