Small Intestinal Bacterial Overgrowth (SIBO) occurs when bacteria from the large intestine colonize the small intestine. The top 10 bacteria commonly associated with SIBO are responsible for many of the clinical side effects of SIBO. The list below shares the most common side effects for each of those 10 SIBO bacteria when overgrown, along with additional clinically relevant details regarding histamine production, autoimmune associations, and other health impacts:
Escherichia coli (E. coli)
- Side Effects: Bloating, abdominal pain, diarrhea, and gas. E. coli overgrowth can also increase the risk of leaky gut syndrome by causing inflammation in the gut lining, leading to a compromised intestinal barrier.
- Clinical Relevance: E. coli is known to release lipopolysaccharides (LPS), which can trigger systemic inflammation. LPS can contribute to autoimmune reactions and has been linked to conditions such as autoimmune thyroiditis (Hashimoto’s disease).
Streptococcus
- Side Effects: Diarrhea, gas, bloating, and abdominal discomfort. Streptococcus can lead to significant inflammation due to the release of bacterial toxins, contributing to digestive disturbances.
- Clinical Relevance: Streptococcus species have been implicated in promoting histamine production, which can exacerbate symptoms of histamine intolerance. Excessive histamine may worsen symptoms in people with Mast Cell Activation Syndrome (MCAS) and food sensitivities.
Lactobacillus
- Side Effects: Gas, bloating, diarrhea, and abdominal discomfort. While typically beneficial in the large intestine, Lactobacillus overgrowth in the small intestine can lead to excessive fermentation.
- Clinical Relevance: Certain strains of Lactobacillus can also produce D-lactate, which can lead to lactic acidosis and neurological symptoms, such as confusion and fatigue. This overgrowth may also contribute to histamine production in some cases, aggravating conditions like MCAS.
Bacteroides
- Side Effects: Abdominal pain, bloating, and diarrhea. Overgrowth of Bacteroides can disrupt the balance of the gut microbiota and contribute to chronic inflammation.
- Clinical Relevance: Bacteroides species are associated with increased production of thyroid antibodies, which can exacerbate autoimmune conditions like Hashimoto’s thyroiditis. They can also influence systemic inflammation and are linked to the development of non-alcoholic fatty liver disease (NAFLD).
Enterococcus
- Side Effects: Bloating, gas, diarrhea, and abdominal pain. Enterococcus overgrowth is associated with chronic gut inflammation and may interfere with normal gut motility.
- Clinical Relevance: Enterococcus is linked to the production of biofilms, which can protect bacterial colonies from both the immune system and antibiotics, making infections harder to treat. It has also been associated with urinary tract infections and is increasingly found to be resistant to antibiotics, including vancomycin-resistant Enterococcus (VRE).
Klebsiella
- Side Effects: Severe bloating, gas, and abdominal pain. Klebsiella species can produce significant amounts of gas and promote inflammation in the gut.
- Clinical Relevance: Klebsiella is strongly associated with autoimmune conditions, particularly ankylosing spondylitis and other spondyloarthropathies. It can trigger molecular mimicry, where the immune system attacks the body’s tissues, mistaking them for bacterial invaders.
Clostridium
- Side Effects: Diarrhea, abdominal cramping, and bloating. Certain species, such as Clostridium difficile, can cause severe inflammation in the gut and colitis.
- Clinical Relevance: Clostridium species, particularly C. difficile, can produce harmful toxins that lead to colitis and severe gut inflammation. Overgrowth of this bacteria is often linked to antibiotic use and can be difficult to treat. Some Clostridium species are associated with increased histamine production, exacerbating symptoms in histamine-sensitive individuals.
Proteus
- Side Effects: Bloating, gas, and diarrhea. Proteus overgrowth contributes to significant digestive disturbances and systemic toxin production.
- Clinical Relevance: Proteus is another biofilm-producing bacteria that can evade immune system attacks. It has been linked to urinary tract infections and can also contribute to kidney stones due to its ability to produce urease, which breaks down urea into ammonia, increasing alkalinity in the urine.
Methanobrevibacter smithii
- Side Effects: Constipation and bloating. This archaea produces methane, which slows intestinal transit time and contributes to constipation.
- Clinical Relevance: Methane production by Methanobrevibacter smithii is linked to constipation-predominant IBS (IBS-C). High methane levels can also correlate with slower motility, leading to a higher risk of SIBO recurrence. Some studies suggest it may also affect thyroid function by slowing gut motility and altering hormone metabolism.
Prevotella
- Side Effects: Bloating, diarrhea, and gas. Overgrowth of Prevotella can disrupt gut balance, leading to inflammation and digestive symptoms.
- Clinical Relevance: Prevotella is commonly linked to chronic inflammatory conditions such as rheumatoid arthritis and periodontitis. It may exacerbate autoimmune responses by triggering systemic inflammation. Prevotella overgrowth has also been observed in individuals with dysbiosis associated with Western diets high in refined carbohydrates.
Summary of Common Side Effects and Clinical Relevance:
- Bloating: Most of these bacteria produce excessive gas through fermentation, leading to bloating and abdominal discomfort.
- Diarrhea: Disruption of digestion can cause frequent, loose stools, often seen with bacteria like E. coli, Streptococcus, and Bacteroides.
- Constipation: Methanobrevibacter smithii is linked to methane production, which slows motility, causing constipation.
- Histamine Production: Bacteria like Streptococcus, Lactobacillus, and Clostridium can contribute to elevated histamine levels, which aggravate conditions like MCAS.
- Autoimmune Associations: Bacteria such as Klebsiella, Bacteroides, and Proteus have strong links to autoimmune conditions, including ankylosing spondylitis, Hashimoto’s thyroiditis, and rheumatoid arthritis.
- Systemic Inflammation: The overgrowth of these bacteria, through mechanisms like LPS release (E. coli) and biofilm production (Enterococcus), can trigger systemic inflammation, leading to conditions such as leaky gut, autoimmune flare-ups, and metabolic disorders.
Managing SIBO with Clinical Insight
Effectively managing SIBO requires not only addressing bacterial overgrowth but also understanding the broader clinical implications each bacterial strain has on the body. Whether through histamine management, addressing autoimmune triggers, or treating systemic inflammation, treating SIBO patients in a holistic manner requires an appreciation and understanding of bacteria’s impact on health.
Our SIBO experts are available to assist Neurovanna healthcare providers with understanding SIBO. Complete our new account form to become a Neurovanna healthcare provider. If you are a patient seeking SIBO care, contact us to find a Neurovanna practitioner near you.
