Small Intestinal Bacterial Overgrowth ( SIBO ) : Result of Altered Defensive Mechanism in Gastrointestinal – A Review

Small intestinal bacterial overgrowth (SIBO) is a condition that is characterized by an increased number of bacteria in the small intestine or an existence of bacteria type that generally should not be in the small intestine. In SIBO, the number of bacteria found in culture was more than 10 5 CFU (Colony-Forming unit) per ml. The fundamental problem in which SIBO occurred was the disruption in defensive mechanisms to prevent bacteria from overgrowing, including gastric acid juice, intestine motility, competent immune function, and intact anatomy. Disruption of this defensive mechanism will lead to SIBO, which furthermore will result in not only mild complications, such as abdominal complaints, but also severe complications, such as maldigestion/malabsorption, nutrient deficiency, or even systemic infection and acidosis. The manifestations of SIBO were often unclear so that it is hard to distinguish with other diseases, which much lead to misdiagnosis or underdiagnosis. Diagnosis of SIBO should be conducted very meticulously regarding underlying diseases that resulted in gastrointestinal defensive mechanism disturbance and malassimilation syndrome. Additional examinations for SIBO currently were jejunal aspiration and breath test, but both of them had their limitations in sensitivity and specificity. Therapeutical management consisted of treating the underlying diseases, eradicating bacteria with the antibiotic, particularly rifaximin, and improving nutritional deficiency.


INTRODUCTION
Small intestinal bacterial overgrowth (SIBO) is a condition that is characterized by an increased number of bacteria in the small intestine or alteration of some type of bacteria that generally should not be in the small intestine. SIBO is characterized by an increased number of bacteria that are found in culture with an amount of 10 5 CFU (Colony-Forming units) per ml. However, there was a literature that doubted this number because the number of bacteria in the small intestine typically should not exceed 10 3 CFU/ml, which meant this number could be offered as another threshold of SIBO. 1,2 SIBO has been associated with some problematic conditions that affect the quality of life, such as malabsorption/maldigestion in the elderly and post large bowel surgery patients 3,4 The underlying mechanism of SIBO until recently is still very complicated. Yet, the most crucial factor that leads to SIBO is the disruption of a homeostatic mechanism that prevents bacterial overgrowth. 1,5 In a healthy condition, a normal flora in the the digestive tract from pathogenic bacteria, perform a metabolic and trophic function, and provide nutrition (short-chain fatty acid). Then, the body itself has other defense mechanisms to prevent the colonization of bacteria in the gastrointestinal tract, including gastric acid and proteolytic enzyme, decent anatomical function, peristaltic movement of the intestine, and a competent immune system. 6 Disruption in this defense system will lead to bacterial colonization and proliferation and small intestine will prompt coliform bacteria to migrate into the small intestine or in chronic PPI users, 4 The problem associated with SIBO is this condition often occurs after some medical interventions such as small intestine surgery, chronic gastric acid suppressor user, and administration of drugs that decrease motility of intestine, like narcotics. Additionally, SIBO could also emerge secondarily because of systemic diseases such as diabetes mellitus, cirrhosis hepatic, scleroderma, and chronic kidney disease. 5 The next problem is to misdiagnose or underdiagnose, yet significantly 1,3 Because SIBO is often associated with many life, so in this literature, SIBO is going to be discussed comprehensively.

EPIDEMIOLOGY
First, for prevalence in SIBO until recently still the prevalence of SIBO in healthy patients is 2.5-22%. 5 SIBO patients usually do not have a symptom or SIBO is usually underdiagnosed. Besides, SIBO often occurs with other diseases such as IBS or celiac disease that make SIBO not diagnosed promptly, and the prevalence of SIBO often varies depending on the conducted examination. 4,5,7 In an examination with hydrogen breath tests on patients with gastrointestinal symptoms, there is 56% of patients positively diagnosed with SIBO while in a study that was conducted in 2003, there was a prevalence of 66% in the patients with celiac disease. 8,9 In another study with different celiac disease patients, prevalence numbers were resulted differently according to applied examination, including jejunal aspiration and breath test, which found as many as 11% and 23%, respectively. 10 Recently, a meta-analysis study showed that the prevalence of SIBO in the IBS population was 38% dan odds of SIBO were increased 11

PATHOPHYSIOLOGY
In the gastrointestinal tract, some mechanisms prevent bacterial overgrowth in intestines such as gastric juice, intestine motility, the competent immune system in the digestive tract, and intact anatomy. Gastric acid has been known to kill and reduce numbers of ingested bacteria, so the number of bacteria Then, in gaster, there are also proteolytic enzymes that help to kill bacteria and mucous layer to detain the bacteria. However, in hypochlorhydria or achlorhydria some bacteria could pass through the stomach. Those cases are often found in H.pylori infection, elderly patients, and chronic gastric acid suppressor users. 12,13 Intestine Motility Motility in the gastrointestinal tract always moves antegrade so that bacteria could not easily attach in the intestine to colonize. Disturbance in motility could lead to ineffective swept of bacteria from proximal intestine to colon, which will allow developing into SIBO. Motility disorder is often found in some metabolic diseases such as diabetes mellitus, cirrhosis hepatic (through retrograde pressure from proximal duodenum), celiac disease, and chronic kidney disease by neuropathy of autonomic nerve. 4,14,15 Altered Immune Function Patients with SIBO usually have immunity alteration in intestine mucous that has been shown by an increased concentration of immunoglobulin A (IgA).
which one of them is SIBO. 5,16 Anatomy Alteration Some anatomy alteration could lead to SIBO are consisted of obstruction and stagnation, a sequel from previous surgery, and short bowel syndrome. Blockage and stagnation, either by stricture, adhesion, diverticula, or tumor, are associated with becoming SIBO. Previously conducted surgery like afferent loop syndrome following gastric surgery, Roux-en-Y, bariatric bypass surgery could lead to SIBO and often accompanied by metabolic disorder because of less optimal food clearance and secretion. Short bowel syndrome could lead to SIBO because an absence ileocaecal valve will yield the migration of coliform bacteria to the intestine and also more undigested food, which is a relevant material to be fermented by bacteria in the intestine. 5,17 Some causes and diseases that lead to abruption of this preventing bacterial overgrowth function are shown in Table 1.
In detail, this process starts when bacteria, particularly coliform bacteria, growth in excessive numbers than generally in the intestine, will yield to as lactose, sucrose, and sorbitol. Then, some of the carbohydrate fermentations will form formations of a short-chain fatty acid, propionate acid, and butyric acid. Although these formations are useful in the colon as a nutrition supplier, in the intestine, these fatty acids will abrupt absorption of nutrients and impair motility by peptide YY, neurotensin, and GLP-1, which aggravate the SIBO itself. 18 These bacteria will also produce some toxic components (peptidoglycans, D-lactate, and serum amyloid A. Fermentation of either carbohydrate or fatty acid, together with the produced toxic components, will lead to an inflammation mucosal damage in the brush border, which will cause permeability disorder in the intestine and probably will lead to protein-losing enteropathy. 19 This permeability Then, these bacteria will deconjugate with a bile salt, which will interfere absorption of fat and generate bacteria will also use protein intraluminal that will excessively. 5,20 function of the gastrointestinal tract but also affect anatomically. Microscopically, there is some alteration in lamina propia and atrophy of intestinal villous. However, macroscopically, there might be ulcer or erosion in the mucous layer of the intestine. Then, these anatomical changes will magnify the symptom of SIBO. 21

CLINICAL MANIFESTATION
Symptoms of SIBO manifestation depend on how severe the disease itself and the underlying conditions. In most cases, SIBO is asymptomatic or shows complaints that similar to IBS, including diarrhea, and abdominal pain. 6 In more severe cases, the symptoms are sometimes accompanied by malabsorption, malnutrition, weight loss, steatorrhea, edema, and other symptoms that are associated encountered in elderly patients because SIBO, until recently, is considered as the leading cause of unexplained diarrhea and maldigestion in elderly patients. 20 The symptoms of SIBO are indeed other diseases like intolerance and IBS. Therefore, SIBO is often misdiagnosed or underdiagnosed. 4 Anemia in SIBO could be microcytic because of a lack of iron either due to gastrointestinal bleeding or due to chronic illness. However, anemia could also be macrocytic because of a lack of vitamin B12 due to the overgrowth of anaerobic bacteria. Vitamin V12 also results in not only polyneuropathy but also other neuropathy complications such as ataxia, speech disorder, and mental status disorder. Lack of vitamin D could result in hypocalcemia so that prompt other disorder such as tetany or bone mineral disease. 5 Other severe complications that could happen yet quite rare are D-lactic acidosis, systemic infection, and worsen liver disease. D-lactic acidosis is a disorder due to the involvement of Lactobacillustype bacteria in SIBO, particularly in a patient with short bowel syndrome. 5 This type of acidosis could also be prompted in SIBO through alcohol and acetaldehyde production that result in alcoholic liver disease. 22 Bacterial translocation is a combination process of SIBO, increased intestine permeability, and immunity alteration so that bacteria could translocate to peritoneum and portal system. Bacterial translocation into the portal system and peritoneum has a more condition is often found in patients with liver diseases. Then, in patients with liver disease as cirrhosis hepatic, SIBO will magnify the state of patients because of encephalopathy hepatic, which will be improved with oral antibiotic administration. 23

MANAGEMENT Diagnosis
Diagnosis of SIBO is a difficult one because while SIBO patients often come with symptoms and diagnosis, probably need to consider it is SIBO if there are abdominal complains that are by with weight loss or malassimilation syndrome, especially on special occasions such as elderly, systemic diseases, history of gastrointestinal surgical, and other cases that affected defense mechanism.
Until recently, no examination has been considered as a gold standard to establish the diagnosis of SIBO. However, there are two additional diagnosis examinations, which are still controversial, to diagnose SIBO, including direct tests by bacterial culture through jejunal aspiration and indirect test through carbohydrate breath tests. 7 Bacterial culture from jejunal aspiration is viewed as an invasive procedure, breath tests, it is a feasible and easy test, but there is still no proper standardization. 24

Direct Test
Examination with bacterial culture as a method to diagnose SIBO needs standardization because, until recently, there has not been established yet. The aspirate sample is collected from the liquid in the proximal jejunum, but some studies recommended to collect samples from upper duodenal because it is more practical dan feasible. 12,24 Diagnosis of SIBO is established if the bacterial colony from the culture is as many as >10 5 CFU/mL. 25 If the bacterial colony is less than 10 5 CFU/mL, SIBO should be considered in case there are species of coliform bacteria. 26 A study in 2008 recommended that coliform bacterial in proximal jejunal that is found more than 10 3 CFU/mL should be fundamental to diagnose SIBO. 2 The limitations of this examination, including contamination from upper gastrointestinal bacteria, unable to reach the distal small intestine, and the difference in place and time of aspiration, will yield many results. Therefore, it sometimes needs multiple sample aspirations. Then, not all types of bacteria could be cultured easily, particularly anaerobic bacteria. 20,24,26,27 Alvin Hartanto Kurniawan, Vania Azalia Gunawan, Benedictus Hanjaya Suwandi, Ulfa Kholili

Indirect Test
A breath test is a non-invasive examination that can be done at a relatively lower price. The hydrogen breath test will depend on hydrogen production from bacterial carbohydrate fermentation in the colon. Most of the produced gas will enter into blood vessels and end at the lungs, where it will be excreted. 7,28 The mechanism of this hydrogen production becomes the basis of the hydrogen breath test examination. The test itself is started by consuming carbohydrates (glucose, lactose, and xylose) orally. Then, the end-expiratory breath will be measured every 15 minutes in 3 hours. Lactulose is the most common carbohydrate to be used in this hydrogen breath test. Because the human body does not break down lactulose so that naturally lactulose will stay in its form through from small intestine to colon and will be fermented by coliform bacteria. 20,28 This examination will be positive if there is both an escalation of hydrogen level > 20 ppm and a double peak in breath hydrogen expiration graph. This double peak is caused by increased gas production and colon. 7,20 If there is no double peak, but there is an early escalation in breath hydrogen test after lactulose consumption (< 90 minutes), that may mean there is bacterial overgrowth. 20 False-positive is often found in the case of carbohydrate malabsorption, digestion by oral bacterial, while false-negative can be seen in a patient with prior antibiotic exposure. 7

Therapeutic Trial
Because of the limitation of both jejunal aspiration test and breath test to diagnose SIBO due to lack countries for both tests, some clinicians approached using therapeutic trials with the empirical antibiotic or rifaximin. However, this method still has not been standardized. Then, if the patients do not respond with the therapeutic trial, it does not mean that the diagnosis of SIBO has been excluded. 5,13,29

Therapy
The therapy principal in SIBO problems emphasizes on three things, which are 1) treat the underlying disease, 2) eradicate bacterial overgrowth, and 3) improve malnutrition and deficiency that follow SIBO. 27 Treat the underlying condition could be conducted in many forms, as dietary change, surgical treatment, or medication treatment. Dietary change can be applied in patients with celiac disease cofounded with SIBO, whereas a strict regimen will result in a better improvement. Additionally, in most of the patients sometimes need to be given a lactose-free diet while increasing energy needs from fat by administrating medium-chain triacylglycerol oils. 5 Surgical should be performed if there is an anatomical alteration that prompts SIBO, such as diverticulosis, 4 In a case of motility disorder of gastrointestinal tracts, like narcotics user or gastroparesis patients, should be administrated with prokinetic agents to increase been proven less effective. 30 In patients with long term PPI use as in GERD patients, dose adjustment is needed as minimum as possible to maintain free of GERD to improve overgrowth symptoms.
Although the underlying disease or disorder that leads to SIBO has been treated, it still mandatory to eradicate overgrowing bacteria by administrating antibiotics. The main target of antibiotic administration not only to eliminate bacteria but also tend to reduce the number 13 Ideally, antibiotic therapy is given selectively to the overgrowth bacteria of each patient based on bacterial sensitivity test against some antibiotics. 31 Nevertheless, this approach is quite tricky because this examination is less sensitive by administrating broad-spectrum antibiotics. However, it is essential to remember that long term administration could lead to diarrhea, the development of , antibiotic resistance, and cost issue. 5 Rifaximin is an antibiotic that has been shown effective in treating SIBO. Rifaximin has been shown to eradicate SIBO up to 80% effectively. 32 Rifaximin is a semi-synthetic form of rifampicin group with low systemic absorption, yet good activity on eradicating bacteria in the gastrointestinal tract. Rifaximin is a chosen antibiotic to deal with the SIBO case because this antibiotic covers all kinds of bacteria. 33 A recent meta-analysis study showed that rifaximin had been succeeded in eradicating bacteria 70.8%, even with improved symptoms of 67.7%. The study also showed that dosage is another critical factor that had been associated with increasing eradication rates. 34 The current recommended dosage for rifaximin in SIBO is 800 mg. However, rifaximin 600 mg, 1200 mg, and 1600 mg were also effective enough to eradicate. The duration of administration that is currently recommended is seven days. 35,36 Additional therapies such as prebiotic or probiotic are still controversial because data about them are still limited and yielded different and contradicting results even though most studies showed that probiotic provides symptoms relief but not the prevention of SIBO. Therefore, more studies are needed for a further recommendation. [37][38][39] Nutritional deficiency improvement is another fundamental part of additional therapy that as important as those two before. Nutritional improvement could be made by administrating vitamin replacement, particularly fat-soluble vitamins and other micronutrient severe mucosal damage, it will probably need a more extended period of nutritional correction although eradication of bacterial overgrowth has been achieved. 13

PROGNOSIS AND COMPLICATION
The prognosis of SIBO varies depending on the severity of the underlying disease that prompts SIBO, as the most severe problem of SIBO is an intestinal failure. 40 Additionally, most of the antibiotic therapy in SIBO is still followed with a recurrence that is shown by a relapse of symptoms, so that they need another review and therapy regimen. Rifaximin has also been reported resistant and recurrence, as shown in a study that found recurrence cases of SIBO that have been treated with rifaximin after nine months are as many as 35/80 patients (44%). Recurrence will be found much more in elderly patients, a history of appendectomy, chronic PPI therapy. 41

CONCLUSION
SIBO is a condition, which consisted of increased abnormal numbers of bacteria or alteration of the bacterial type in the intestine. SIBO is associated with some diseases that affected protection to bacterial overgrowths, such as intestine motility, gastric acid, competent immune system, and free of anatomy alteration. The symptoms that occur in SIBO vary from mild (bloating) to severe, for example, decreased establishing a diagnosis still becomes a primary focus to develop because of limitations in sensitivity and specificity. The therapy approach is attempted in 3 principals, resolve underlying disease, eradicate