Small intestinal bacterial overgrowth is described as the accumulation of a large number of bacteria in this organ, which should not normally be located in the structure. There are often underlying diseases and factors associated with the development of this condition.
The clinical picture is variable. Some patients will present with symptoms, while other will feature resemblance to IBS. According to studies that investigated the chief features of SIBO, there is a consequential sequence of diarrhea, abdominal pain, and then bloating.
Note that most studies did not use validated questionnaires to identify symptoms, therefore, the details are lacking.
An important aspect of the overall patient presentation is malabsorption and the resultant signs. Examples include weight loss and deficiencies in fat soluble vitamins and folate. Furthermore, nutritional deficiencies may occur due to the malabsorption of fat, carbohydrates, and protein. The symptoms associated are bloating, cramping, diarrhea, anorexia, and weight loss.
In patients with vitamin D deficiency, there are risks for the development of osteomalacia, hypocalcemia and osteoporosis. The latter is a known sequela of SIBO. Additionally, the lack of vitamin E may lead to neuropathy.
Vitamin B12 deficiency causes megaloblastic, macrocytic anemia and polyneuropathy. This vitamin deficiency likely results from the utilization of the vitamin by facultative Gram-negative aerobes and anaerobes.
One investigation involves the proper assessment of the stomach and small bowel through gastroscopy and a biopsy. The findings may resemble those of celiac disease, which includes villous blunting, crypt hyperplasia, and increased lymphocytes in the lamina propria.
The gold standard test for SIBO is the identification of at least 105 bacteria per milliliter of jejunal aspirates, as the small intestine normally has less than 104 bacteria per milliliter. There is some doubt about the reliability of this test since SIBO can be patchy. Also, the findings may not be reproducible.
Another study is the D-xylose test, in which the patient drinks xylose, a sugar that is not digested by enzymes. After consumption, the D-xylose levels are measured in the blood and urine. The absence of the sugar indicates malabsorption.
Further investigations include breath tests that are designed to assess bacterial overgrowth. In the hydrogen breath test, the individual drinks glucose or lactulose, following a period of a 12 hour fast. Afterward, the hydrogen and methane levels are measured from the patient's expired breath. Similarly, the glycocholic acid breath test uses the bile acid for the detection of 14CO2, which is increased in cases of excessive bacterial growth. Note that these tests face questions regarding their reliability since there is a high rate of false positives.
Clinicians may implement a treatment trial to confirm the diagnosis in cases highly suggestive of SIBO. An improvement of symptoms indicates SIBO.
The treatment of SIBO should be directed at the etiology if possible, which may be an underlying disorder or a structural abnormality. The main therapeutic approaches are antibiotic use, probiotic therapy, and correction of nutritional deficiencies.
Therapy may consist of bacterial overgrowth correction with empiric antibiotics aimed at the treatment of aerobic and anaerobic enterobacteria. While there is no specific regimen, the options are metronidazole, ciprofloxacin, neomycin, norfloxacin, and doxycycline. Furthermore, one study demonstrated that more than 90% of strains in SIBO patients were eliminated by the combination of cefoxitin and amoxicillin–clavulanic acid. Additionally, ciprofloxacin exhibited strong activity in 70% of cases. Another drug, rifaximin, may be beneficial in patients with both SIBO and IBS as it is efficacious in IBS.
The clinician should be vigilant about the bacterial resistance and side effects when considering and selecting antibiotic management.
These agents may be useful in SIBO patients. One pilot trial evaluated the outcome of Lactobacillus casei Shirota in patients with SIBO diagnosed by a positive hydrogen test. Following a 6-week period of therapy with this probiotic, 64% of the patients exhibited a negative breath test although symptomatic improvement was not remarkable.
Another pilot investigation compared probiotic use versus metronidazole therapy. The trial noted that probiotics demonstrated greater success in symptom management, in comparison to metronidazole. To corroborate this result, a randomized, double-blinded placebo controlled investigation is necessary to provide further information.
Fluids and nutrition
Also, the proper assessment and management of osteoporosis are warranted, as this is a recognized complication of SIBO.
The prognosis of SIBO is usually related to the cause of the condition and other factors, such as the ensuing consequences.
The most common cause of death is liver failure due to the parenchymal destruction in this organ. Other reasons linked to the fatality of SIBO patients are the decreased venous access or complications of severe sepsis.
There is a high mortality rate with the post-surgical complications. In survivors, up to 90% will remain alive after one year and about 60% will reach the 4-year mark.
In the newborn population receiving total parenteral nutrition (TPN), almost 70% will achieve a 4-year survival rate while about 20% will reach the 5-year survival point.
The causes of SIBO are typically convoluted, as it is related to many diseases that affect the physiologic antibacterial mechanisms. These endogenous processes that restrict the growth of bacteria are 1) intestinal motility, 2) gastric acid secretion, 3) the ileocecal valve, 4) the presence of antibiotic substances in pancreatic and biliary secretions, and 5) the presence of immunoglobulins in intestinal secretions .
The disorders that affect these mechanisms may lead to SIBO. For example, etiologies of this condition include motility disorders such as diabetes-induced autonomic neuropathy, scleroderma, etc. Additionally, anatomical defects such as the resection of the ileocecum, small bowel obstruction, fistulas, diverticula, and surgical loops can cause bacterial overgrowth. Finally, achlorhydria and pancreatic exocrine insufficiency may contribute to the development of SIBO, as do immunodeficiency diseases.
Note that small bowel motility disorders and chronic pancreatitis account for 90% of cases .
The causes and risk factors may be the same in patients. Also, some individuals have numerous predisposing factors for SIBO. Adding to the complexity of the condition, the underlying pathology may contribute to the development of SIBO, which in turn complicates the disease further.
The prevalence of SIBO, in general, has not been established. This condition is typically under-diagnosed, as it does not always cause symptoms, and when it does, they are nonspecific or are attributed to underlying disorders.
Certain investigations evaluated the occurrence of SIBO. The condition was observed in 2.5% to 22% in studies that used healthy subjects as the control . Also, the frequency of SIBO varies from one disease to another according to literature. For example, 30% to 85% of patients with irritable bowel syndrome (IBS) have SIBO . Bacterial overgrowth is found in up to 50% of celiac disease cases , greater than 50% of patients with liver cirrhosis , and 90% of elderly individuals with lactose intolerance . Additionally, one investigation reported that the condition was demonstrated in 17% of asymptomatic obese patients versus 2.5% of non-obese subjects .
The antibacterial mechanisms that control bacterial growth can be disrupted when there is decreased gastric acid secretion or small bowel immobility. Regarding the latter, the migrating motor complex (MMC) is responsible for the flow of bacteria into the large bowel during periods of fasting,
Other protective mechanisms include the functional ileocaecal valve, the production of immunoglobulins in intestinal secretions and antibacterial properties in pancreatic and biliary secretions.
Procedures such as a gastrectomy can create loops of small bowel that house excess bacteria.
Immunodeficient individuals exhibit a high prevalence of SIBO. These patients have profoundly elevated immunoglobulin A in the duodenal and jejunal mucosa.
Findings in SIBO
Excessive production of bacteria can activate an inflammatory reaction in the mucosal layer of the bowel. This may be demonstrated in microscopic examination, although this is not always necessary . Furthermore, the biopsy findings associated with SIBO in elderly patients are blunting of the villi, thinning of crypts and the mucous layer and increased amounts of lymphocytes . These changes are corrected with antibiotic therapy .
The recurrence of SIBO is common, since the elimination of the overgrowth will not cure the underlying disease.
Treatment with probiotics or antibiotics does not prevent the relapse, as bacteria can accumulate within 2 weeks of completion of these agents. Therefore, one protocol outlines preventive strategies, which include 1) the use of a pro-motility drug to stimulate the MMC, 2) adherence to a continuous SIBO diet, low in carbohydrates, 3) treatment of coexisting diseases contributing to SIBO, 4) patients with Hydrochloric Acid (HCl) deficiency should receive supplementation with this acid, 5) withdrawal of proton pump inhibiting drugs (PPIs) and antacids, 6) treatment of neurological disorders, and 7) repair of Ileocecal Valve Syndrome (IVC) to prevent the bacterial backflow into the small bowel.
Note that prokinetic drugs and a proper diet are crucial in the prevention of SIBO recurrence.
Small intestinal bacterial overgrowth (SIBO) is characterized by excessive numbers and/or change in the type of bacteria in an organ. The complex flora of the human gastrointestinal tract features a delicate balance that is protected by normal physiologic and anatomical mechanisms. Hence, any disruption to these processes can result in serious alterations in the health of the patient. Furthermore, the etiology is typically complicated and may be associated with various factors.
The clinical presentation may fluctuate, as some patients will not exhibit symptoms while others feature manifestations such as weight loss, diarrhea, abdominal pain, and bloating. Additionally, SIBO may give rise to complications such as osteoporosis and fat-soluble vitamin deficiencies.
The clinical assessment for patients suspected to have SIBO consists of a detailed medical and surgical history, physical exam, and particular studies, such as the gold standard investigation of jejunal aspirates. Moreover, the criteria for diagnosis is the result of 10^5 bacteria or more per milliliter of aspiration   . Other tests include non-invasive methods, such as breath tests.
The therapeutic goal is to treat the cause, if possible. The exact management is tailored for the particular patient and may warrant the use of antibiotics and/or probiotics. Additionally, vitamin and nutritional deficiencies, as well as other sequelae should be addressed.
Small intestine bacterial overgrowth (SIBO) is a disorder described by the production of large bacterial populations in the small intestine.
What are the causes of SIBO?
There are numerous conditions and diseases that can cause this excessive growth of bacteria in the small intestine such as:
What are the symptoms?
In addition to weight loss, the patients may experience gastrointestinal disturbances such as:
What are some of the complications?
Normally, the small intestine does not have large numbers of bacteria like the large intestine does. Therefore, the many bacteria use up nutrients and vitamins that the body would otherwise use for itself. This is why patients with SIBO will become malnourished. Patients may also develop dehydration, liver disease, and osteoporosis.
How is this condition diagnosed?
The clinician will evaluate the signs and symptoms and assess the full medical and surgical history. Also, they will perform a physical exam and obtain important test, such as small intestine biopsy and aspirates, breath tests, abdominal x-rays, stool fat test, complete blood count (CBC), blood chemistry levels, and vitamin levels.
How is SIBO treated?
The aim of the treatment is to target the overgrowth of the bacteria and is usually tailored to the specific patient. This may consist of antibiotics, probiotics, and/or medications that increase the movement in the small intestine. These patients are also encouraged to follow a specific diet with low amounts of carbohydrate.
Another aspect of the therapy includes providing the patients with fluids and nutrition. Dehydrated and malnourished patients should be treated with intravenous fluids and total parenteral nutrition (TPN).
How can SIBO be prevented?
Promotility drugs can help to prevent further episodes of this condition from developing. Also, a SIBO friendly diet is considered important. The doctor may decide to take other measures such as stopping antacids and maybe even surgery to repair anatomical abnormalities.