From the Guidelines
The root cause of Small Intestinal Bacterial Overgrowth (SIBO) is a disruption in the normal protective mechanisms that prevent excessive bacterial growth in the small intestine, typically due to impaired intestinal motility, which allows bacteria to accumulate rather than being swept through the digestive tract. Several underlying conditions can lead to this motility disruption, including diabetes, scleroderma, hypothyroidism, and previous abdominal surgeries that may create structural abnormalities. Other contributing factors include insufficient stomach acid (hypochlorhydria), which normally helps control bacterial populations; immune system deficiencies that compromise the body's ability to regulate intestinal bacteria; and damage to the migrating motor complex, the cleansing wave mechanism that moves contents through the digestive tract between meals. Certain medications like proton pump inhibitors, opioids, and antibiotics can also disrupt the normal bacterial balance, as noted in a study on the management of adult patients with severe chronic small intestinal dysmotility 1.
While SIBO itself is characterized by bacterial overgrowth, identifying and addressing these underlying causes is essential for effective treatment and preventing recurrence, rather than simply treating the bacterial overgrowth alone. The relationship between SIBO and other gastrointestinal conditions, such as inflammatory bowel disease (IBD), has been explored in recent studies, including a systematic review with meta-analysis that showed a substantial increase in the prevalence of SIBO in IBD with prior surgery and the presence of fibrostenosing disease as risk factors 1.
Key factors to consider in the development of SIBO include:
- Impaired intestinal motility
- Insufficient stomach acid (hypochlorhydria)
- Immune system deficiencies
- Damage to the migrating motor complex
- Certain medications (proton pump inhibitors, opioids, antibiotics)
- Underlying conditions (diabetes, scleroderma, hypothyroidism, previous abdominal surgeries)
In the context of chronic pancreatitis, SIBO may complicate the condition in up to 92% of patients, with symptoms that may be confused with those of the underlying disease, as discussed in a study on negotiating the complexities of exocrine and endocrine dysfunction in chronic pancreatitis 1. Therefore, addressing the underlying causes of SIBO and considering the potential for SIBO in patients with chronic pancreatitis or other gastrointestinal conditions is crucial for effective management and prevention of recurrence.
From the Research
Definition and Aetiology of SIBO
- SIBO is defined as an increase in the number and/or alteration in the type of bacteria in the upper gastrointestinal tract 2.
- The aetiology of SIBO is usually complex, associated with disorders of protective antibacterial mechanisms, anatomical abnormalities, and/or motility disorders 2.
- Endogenous defence mechanisms for preventing bacterial overgrowth include gastric acid secretion, intestinal motility, intact ileo-caecal valve, immunoglobulins within intestinal secretion, and bacteriostatic properties of pancreatic and biliary secretion 2.
Risk Factors for SIBO
- Hypochlorhydria, disorders of intestinal structure or motor function, pancreatic insufficiency, and chronic liver disease are well-known risk factors for SIBO 3.
- Other risk factors may include achlorhydria, immunodeficiency syndromes, small intestinal obstruction, diverticula, fistulae, surgical blind loop, and previous ileo-caecal resections 2.
Diagnosis and Treatment of SIBO
- The gold standard for diagnosing SIBO is microbial investigation of jejunal aspirates, while non-invasive hydrogen and methane breath tests are commonly used for diagnosis 2.
- Therapy for SIBO must be complex, addressing all causes, symptoms, and complications, and fully individualised, including treatment of the underlying disease, nutritional support, and cyclical gastrointestinal selective antibiotics 2.
- Rifaximin has been shown to be effective and safe in eradicating SIBO, with a dose-dependent efficacy and commonly associated with the improvement of gastrointestinal symptoms and underlying diseases 4.