Small intestinal bacterial overgrowth (SIBO), also termed bacterial overgrowth, or small bowel bacterial overgrowth syndrome (SBBOS), is a disorder of excessive

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

l growth in the

small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

. Unlike the colon (or large bowel), which is rich with bacteria, the small bowel usually has fewer than 100,000 organisms per millilitre. Patients with SIBO typically develop symptoms which may include

nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. It can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat. Over 30 d ...

bloating Abdominal bloating (or simply bloating) is a short-term disease that affects the gastrointestinal tract. Bloating is generally characterized by an excess buildup of gas, air or fluids in the stomach. A person may have feelings of tightness, pressu ...

vomiting Vomiting (also known as emesis, puking and throwing up) is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteritis, pre ...

diarrhea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...

malnutrition Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is a deficiency, excess, or imbalance of energy, protein and other nutrients which adversely affects the body's tissues a ...

weight loss Weight loss, in the context of medicine, health, or physical fitness, refers to a reduction of the total body mass, by a mean loss of fluid, body fat (adipose tissue), or lean mass (namely bone mineral deposits, muscle, tendon, and other conn ...

, and

malabsorption Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal (GI) tract. Impairment can be of single or multiple nutrients depending on the abnormality. This may lead to malnutrition and a varie ...

by various mechanisms. The

diagnosis Diagnosis (: diagnoses) is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in a lot of different academic discipline, disciplines, with variations in the use of logic, analytics, and experience, to determine " ...

of SIBO is made by several techniques, with the

gold standard A gold standard is a backed currency, monetary system in which the standard economics, economic unit of account is based on a fixed quantity of gold. The gold standard was the basis for the international monetary system from the 1870s to the ...

being an aspirate from the

jejunum The jejunum is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been pr ...

that grows more than 10⁵

per millilitre.

Risk factor In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection. Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often use ...

s for the development of SIBO include dys

motility Motility is the ability of an organism to move independently using metabolism, metabolic energy. This biological concept encompasses movement at various levels, from whole organisms to cells and subcellular components. Motility is observed in ...

;

anatomical Anatomy () is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old scien ...

disturbances in the bowel, including

fistula In anatomy, a fistula (: fistulas or fistulae ; from Latin ''fistula'', "tube, pipe") is an abnormal connection (i.e. tube) joining two hollow spaces (technically, two epithelialized surfaces), such as blood vessels, intestines, or other h ...

diverticula In medicine or biology, a diverticulum is an outpouching of a hollow (or a fluid-filled) structure in the body. Depending upon which layers of the structure are involved, diverticula are described as being either true or false. In medicine, t ...

and blind loops created after surgery, and resection of the ileo-cecal valve;

gastroenteritis Gastroenteritis, also known as infectious diarrhea, is an inflammation of the Human gastrointestinal tract, gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of ...

-induced alterations to the small intestine; and the use of certain medications, including

proton pump inhibitors Proton-pump inhibitors (PPIs) are a class of medications that cause a profound and prolonged reduction of gastric acid, stomach acid production. They do so by irreversibly inhibiting the stomach's H+/K+ ATPase, H+/K+ ATPase proton pump. The body ...

. SIBO is treated with an elemental diet or

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

s, which may be given cyclically to prevent tolerance to the antibiotics, sometimes followed by prokinetic drugs to prevent recurrence if dysmotility is a suspected cause.

Definition

SIBO may be defined as an increased number of bacteria measured via exhaled hydrogen and/or methane gas following the ingestion of

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

, or via analysis of small bowel aspirate fluid. Nevertheless, as of 2020, the definition of SIBO as a clinical entity lacks precision and consistency; it is a term generally applied to a clinical disorder where symptoms, clinical signs, and/or laboratory abnormalities are attributed to changes in the numbers of bacteria or the composition of the bacterial population in the small intestine. The main obstacle to accurately defining SIBO is limited understanding of the normal intestinal microbial population. Future advances in sampling technology and techniques for counting bacterial populations and their metabolites should provide much-needed clarity.

Methane-dominant SIBO

The

archaeon Archaea ( ) is a domain of organisms. Traditionally, Archaea only included its prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even though the domain Archaea cladis ...

Methanobrevibacter smithii ''Methanobrevibacter smithii'' is the predominant methanogenic archaeon in the microbiota of the human gut. ''M. smithii'' has a coccobacillus shape. It plays an important role in the efficient digestion of polysaccharides (complex sugars) b ...

'' has been associated with symptoms of SIBO, which result in a positive methane breath test. In addition to the

, a few bacteria can also produce methane, such as members of the ''Clostridium'' and ''Bacteroides'' genus. Production of methane, therefore, may not be bacterial, nor limited to the small intestine, and it has been proposed that the condition should be classified as a separate 'intestinal

methanogen Methanogens are anaerobic archaea that produce methane as a byproduct of their energy metabolism, i.e., catabolism. Methane production, or methanogenesis, is the only biochemical pathway for Adenosine triphosphate, ATP generation in methanogens. A ...

overgrowth' (IMO).

Signs and symptoms

Symptoms traditionally linked to SIBO include

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The Human feces, stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the ...

, and abdominal pain/discomfort.

Steatorrhea Steatorrhea (or steatorrhoea) is the presence of excess fat in Human feces, feces. Stools may be bulky and difficult to flush, have a pale and oily appearance, and can be especially foul-smelling. An oily anal leakage or some level of fecal incon ...

may be seen in more severe cases. SIBO can cause a variety of

symptom Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

s, many of which are also found in other conditions, making the

challenging at times. Many of the symptoms are due to

of nutrients due to the effects of bacteria, which either metabolize nutrients or cause inflammation of the small bowel, impairing absorption. The symptoms of SIBO include

flatus Flatulence is the expulsion of gas from the intestines via the anus, commonly referred to as farting. "Flatus" is the medical word for gas generated in the stomach or bowels. A proportion of intestinal gas may be swallowed environmental air, ...

, bloating, abdominal distension, abdominal pain or discomfort, diarrhea, fatigue, and weakness. SIBO also causes an increased permeability of the small intestine. Some patients may lose weight. Children with SIBO may develop

and have difficulty attaining proper growth.

, a sticky type of diarrhea where

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers specif ...

is not properly absorbed and spills into the stool, may also occur. People with long-term SIBO may develop complications as a result of malabsorption of nutrients. Blood tests may show increased level of

folate Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and ...

(vitamin B₉). Less commonly, there may be

vitamin B₁₂ deficiency Vitamins are organic molecules (or a set of closely related molecules called vitamers) that are essential to an organism in small quantities for proper metabolic function. Essential nutrients cannot be synthesized in the organism in suff ...

or other nutritional deficiencies. The combination of elevated folate and low vitamin B₁₂ is unusual.

Anemia Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availabl ...

may occur from a variety of mechanisms, as many of the nutrients involved in the production of

red blood cell Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...

s are absorbed in the affected small bowel.

Iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

is absorbed in the more proximal parts of the small bowel, the

duodenum The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

and

, and patients with malabsorption of iron can develop a microcytic anemia, with small red blood cells. Vitamin B₁₂ is absorbed in the last part of the small bowel, the

ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...

, and patients who have malabsorption of vitamin B₁₂ can develop a

megaloblastic anemia Megaloblastic anemia is a type of macrocytic anemia. An anemia is a red blood cell defect that can lead to an undersupply of oxygen. Megaloblastic anemia results from inhibition of DNA replication, DNA synthesis during red blood cell production. ...

with large red blood cells.

Causes

Certain people are more predisposed to the development of SIBO because of certain risk factors. These factors can be grouped into four categories: (1)

disorders, impaired movement of the small bowel, or anatomical changes that lead to stasis (a state in which the normal flow of a body liquid stops); (2) disorders of the

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

; (3) interference with the production of proteolytic enzymes, gastric acid, or bile; and (4) conditions that cause more bacteria from the colon to enter the

small bowel The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

. Absence or impairment of the

migrating motor complex Migrating motor complex, also known as migrating myoelectric complex, migratory motor complex, migratory myoelectric complex and MMC, is a cyclic, recurring motility pattern that occurs in the stomach and small bowel during fasting; it is interrupte ...

(MMC), a cyclical motility pattern in the small intestine, and phase III of the MMC in particular, is associated with the development of SIBO. Problems with motility may either be diffuse or localized to particular areas. MMC impairment may be a result of post-infectious IBS, drug use, or intestinal pseudo-obstruction among other causes. There is an overlap in findings between

tropical sprue Tropical sprue is a malabsorption disease commonly found in tropical regions, marked with abnormal flattening of the villi and inflammation of the lining of the small intestine. It differs significantly from coeliac sprue. It appears to be a mor ...

, post-infectious IBS and SIBO in the pathophysiology of the three conditions and also SIBO can similarly sometimes be triggered by an acute gastrointestinal infection. As of 2020, there is still controversy about the role of SIBO in the pathogenesis of common functional symptoms such as those considered to be components of IBS. Diseases like

scleroderma Scleroderma is a group of autoimmune diseases that may result in changes to the skin, blood vessels, muscles, and internal organs. The disease can be either localized to the skin or involve other organs, as well. Symptoms may include areas ...

cause diffuse slowing of the bowel, leading to increased bacterial concentrations. More commonly, the small bowel may have anatomical problems, such as out-pouchings known as

that can cause bacteria to accumulate. After surgery involving the

stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...

and

(most commonly with Billroth II antrectomy), a ''blind loop'' may be formed, leading to stasis of flow of intestinal contents. This can cause overgrowth, and is termed ''

blind loop syndrome Blind loop syndrome, also known as stagnant loop syndrome, is a state that occurs when the normal bacterial flora of the small intestine proliferates to numbers that cause significant derangement to the normal physiological processes of digestion ...

''. Systemic or metabolic disorders may lead to conditions allowing SIBO as well. For example, diabetes can cause intestinal neuropathy,

pancreatitis Pancreatitis is a condition characterized by inflammation of the pancreas. The pancreas is a large organ behind the stomach that produces digestive enzymes and a number of hormone A hormone (from the Ancient Greek, Greek participle , "se ...

, leading to pancreatic insufficiency can impair digestive enzyme production, and bile may be affected as part of

cirrhosis of the liver Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, chronic liver failure or chronic hepatic failure and end-stage liver disease, is a chronic condition of the liver in which the normal functioning tissue, or parenchyma, is replaced ...

. The use of

, a class of medication used to reduce stomach acid, is associated with an increased risk of developing SIBO. Finally, abnormal connections between the

-rich colon and the small bowel can increase the bacterial load in the small bowel. Patients with

Crohn's disease Crohn's disease is a type of inflammatory bowel disease (IBD) that may affect any segment of the gastrointestinal tract. Symptoms often include abdominal pain, diarrhea, fever, abdominal distension, and weight loss. Complications outside of the ...

or other diseases of the

may require surgery that removes the

ileocecal valve In many Animalia, including humans, an ileocolic structure or problem is something that concerns the region of the gastrointestinal tract from the ileum to the large intestine, colon. In Animalia that have cecum, ceca, the ileocecal region is a sub ...

connecting the small and large bowel; this leads to an increased reflux of bacteria into the small bowel. After

bariatric surgery Bariatric surgery (also known as metabolic surgery or weight loss surgery) is a surgical procedure used to manage obesity and obesity-related conditions. Long term weight loss with bariatric surgery may be achieved through alteration of gut ho ...

for obesity, connections between the stomach and the

can be formed, which may increase bacterial load in the small bowel.

Related conditions

In recent years, several proposed links between SIBO and other disorders have been made. Usually, such research uses breath testing as an indirect investigation for SIBO.

Irritable bowel syndrome

Some studies reported that up to 80% of patients with

irritable bowel syndrome Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating, and changes in the consistency of bowel movements. These symptoms may ...

(IBS) have SIBO (using the

hydrogen breath test A hydrogen breath test (HBT) or hydrogen-methane breath test is a breath test used as a diagnostic tool for small intestine bacterial overgrowth (SIBO), and carbohydrate malabsorption, such as lactose, fructose, and sorbitol malabsorption. The ...

). IBS-D is associated with elevated hydrogen numbers on breath tests, while IBS-C is associated with elevated methane numbers on breath tests. Subsequent studies demonstrated statistically significant reduction in IBS symptoms following therapy for SIBO. Various mechanisms are involved in the development of diarrhea and IBS-D in SIBO. First, the excessive bacterial concentrations can cause direct inflammation of the small bowel cells, leading to an inflammatory diarrhea. The malabsorption of

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s, and

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

s may cause poorly digestible products to enter the large bowel. This can cause an osmotic diarrhea or stimulate the colonic cells to cause a secretory diarrhea. There is a lack of consensus regarding the suggested link between IBS and SIBO. Other authors concluded that the abnormal breath results so common in IBS patients do not suggest SIBO, and state that "abnormal fermentation timing and dynamics of the breath test findings support a role for abnormal intestinal bacterial distribution in IBS." There is consensus that breath tests are abnormal in IBS; however, the disagreement lies in whether this is representative of SIBO.

Diagnosis

D-xylose absorption test

Malabsorption Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal (GI) tract. Impairment can be of single or multiple nutrients depending on the abnormality. This may lead to malnutrition and a varie ...

can be detected by a test called the

D-xylose absorption test D-xylose absorption test is a medical test performed to diagnose conditions that present with malabsorption of the proximal small intestine due to defects in the integrity of the gastrointestinal mucosa.Xylose Xylose ( , , "wood") is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional group. It is deriv ...

is a sugar that does not require enzymes to be digested. The D-xylose test involves having a patient drink a certain quantity of D-xylose, and measuring levels in the

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

and

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...

; if there is no evidence of D-xylose in the

and

, it suggests that the small bowel is not absorbing properly (as opposed to problems with enzymes required for digestion).

Small bowel aspirate culture

The

for detection of SIBO is aspiration and

culture Culture ( ) is a concept that encompasses the social behavior, institutions, and Social norm, norms found in human societies, as well as the knowledge, beliefs, arts, laws, Social norm, customs, capabilities, Attitude (psychology), attitudes ...

of fluid from the jejunum. More than 10⁵

colony-forming units In microbiology, a colony-forming unit (CFU, cfu or Cfu) is a unit which estimates the number of microbial cells (bacteria, fungi, viruses etc.) in a sample that are viable, able to multiply via binary fission under the controlled conditions. Coun ...

(more than 100,000 bacteria) per milliliter from the small bowel suggests SIBO. The normal small bowel has less than 10⁴ bacteria per millilitre. However, some experts consider aspiration of more than 10³ positive if the flora is predominantly colonic-type bacteria, as these types of bacteria are considered pathological in excessive numbers in the small intestine. The reliability of aspiration in the diagnosis of SIBO has been questioned, as SIBO can be patchy, and the reproducibility can be as low as 38%. Some doctors factor in a patient's response to treatment as part of the diagnosis.

Breath tests

Breath tests for SIBO are either based on bacterial metabolism of

carbohydrates A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ma ...

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

, or

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

; or based on the detection of by-products of the digestion of carbohydrates that are not usually metabolized. The

involves having the patient fast for a minimum of 12 hours, then having them drink a substrate, usually glucose or

lactulose Lactulose is a non-absorbable sugar used in the treatment of constipation and hepatic encephalopathy. It is administered orally for constipation, and either orally or rectally for hepatic encephalopathy. It generally begins working after 8� ...

, then measuring expired hydrogen and methane concentrations typically over several hours. It compares well to jejunal aspirates in making the diagnosis of SIBO.

Carbon-13 Carbon-13 (13C) is a natural, stable isotope of carbon with a nucleus containing six protons and seven neutrons. As one of the environmental isotopes, it makes up about 1.1% of all natural carbon on Earth. Detection by mass spectrometry A m ...

(¹³C) and

carbon-14 Carbon-14, C-14, C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic matter is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...

(¹⁴C) based tests have also been developed based on the bacterial metabolism of D-xylose. Increased bacterial concentrations are also involved in the deconjugation of bile acids. The

glycocholic acid Glycocholic acid, or cholylglycine, is a crystalline bile acid involved in the emulsification of fats. It occurs as a sodium salt in the bile of mammals. It is a conjugate of cholic acid with glycine. Its anion is called glycocholate. In a pr ...

breath test involves the administration of the bile acid ¹⁴C glycocholic acid, and the detection of ¹⁴CO₂, which would be elevated in SIBO. Breath tests may be an imperfect test for SIBO. In some people, methanogens may reside in the mouth, as evidenced by reductions in breath methane levels following mouthwash with

chlorhexidine Chlorhexidine is a disinfectant and antiseptic which is used for skin disinfection before surgery and to disinfect surgical instruments. It is also used for cleaning wounds, preventing dental plaque, treating yeast infections of the mouth, and ...

. This may affect results from hydrogen-methane breath testing. Breath tests give multiple

false positives A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test res ...

(a positive test result when in reality the person does not have the condition). On the other hand, breath tests are commonly used because they are non invasive and not expensive.

Other diagnostic methods

Some physicians suggest that if the suspicion of SIBO is high enough, the best diagnostic test is a trial of treatment. If the symptoms improve, an empiric diagnosis of SIBO can be made. There is insufficient evidence to support the use of inflammatory markers, such as fecal calprotectin, to detect SIBO.

Treatment

Treatment strategies should focus on identifying and correcting the root causes, resolving nutritional deficiencies, and administering antibiotics. This is especially important for patients with indigestion and malabsorption. Whether antibiotics should be a first-line treatment is debated. Some experts recommend

probiotics Probiotics are live microorganisms that provide health benefits when consumed, generally by improving or restoring the microbiota in the Gut microbiota, gut. Probiotics are considered GRAS, generally safe to consume, but may cause bacteria– ...

as first-line therapy, with antibiotics reserved as a second-line treatment for more severe cases of SIBO. Prokinetic drugs are other options, but human research is limited. A variety of antibiotics, including

tetracycline Tetracycline, sold under various brand names, is an antibiotic in the tetracyclines family of medications, used to treat a number of infections, including acne, cholera, brucellosis, plague, malaria, and syphilis. It is available in oral an ...

, amoxicillin-clavulanate,

metronidazole Metronidazole, sold under the brand name Flagyl and Metrogyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vagino ...

neomycin Neomycin, also known as framycetin, is an aminoglycoside antibiotic that displays bactericidal activity against Gram-negative aerobic bacilli and some anaerobic bacilli where resistance has not yet arisen. It is generally not effective against ...

cephalexin Cefalexin, also spelled cephalexin, is an antibiotic that can treat a number of bacterial infections. It kills gram-positive bacteria, gram-positive and some gram-negative bacteria by disrupting the growth of the bacterial cell wall. Cefalexi ...

and

trimethoprim-sulfamethoxazole Trimethoprim/sulfamethoxazole, sold under the trade names Bactrim, Cotrim (a short form of the British Approved Name, Co-trimoxazole) and Septra, among others, is a fixed-dose combination antibiotic medication used to treat a variety of bacte ...

have been used; however, the best evidence is for the use of

rifaximin Rifaximin is a non-absorbable, broad-spectrum antibiotic mainly used to treat travelers' diarrhea. It is based on the rifamycin antibiotics family. Since its approval in Italy in 1987, it has been licensed in more than 30 countries for the t ...

, a poorly-absorbed antibiotic. Although IBS has been shown to respond to the treatment of poorly-absorbed antibiotics, there is limited evidence on the effectiveness of such treatment in cases of SIBO, and as of 2020, randomized controlled trials are still needed to confirm the eradicating effect of such treatment in SIBO. A course of one week of antibiotics is usually sufficient to treat the condition. However, if the condition recurs, antibiotics can be given cyclically to prevent tolerance. For example, antibiotics may be given for a week, followed by three weeks off antibiotics, followed by another week of treatment. Alternatively, the choice of antibiotic used can be cycled. There is still limited data to guide the clinician in developing antibiotic strategies for SIBO. Therapy remains, for the most part, empiric. However, concerns exist about the potential risks of long-term broad-spectrum antibiotic therapy.

Probiotic Probiotics are live microorganisms that provide health benefits when consumed, generally by improving or restoring the microbiota in the gut. Probiotics are considered generally safe to consume, but may cause bacteria– host interactions ...

s are bacterial preparations that alter the bacterial flora in the bowel to cause a beneficial effect. Animal research has demonstrated that probiotics have barrier-enhancing, antibacterial, immune-modulating, and anti-inflammatory effects, which may have a positive effect in the management of SIBO in humans. ''

Lactobacillus casei ''Lacticaseibacillus casei'' is an organism that belongs to the largest genus in the family ''Lactobacillaceae'', a lactic acid bacteria (LAB), that was previously classified as ''Lactobacillus casei''. This bacteria has been identified as fac ...

'' is effective in improving breath hydrogen scores after six weeks of treatment, presumably by suppressing levels of a small intestinal SIBO of fermenting bacteria. ''

Lactobacillus plantarum ''Lactiplantibacillus plantarum'' (formerly ''Lactobacillus arabinosus'' and ''Lactobacillus plantarum'') is a widespread member of the genus ''Lactiplantibacillus'' and commonly found in many fermented food products as well as anaerobic plant ma ...

'', ''Lactobacillus acidophilus'', and ''Lactobacillus casei'' have all demonstrated effectiveness in the treatment and management of SIBO. Conversely, ''

Lactobacillus fermentum ''Limosilactobacillus fermentum'' is a Gram-positive species in the heterofermentative genus ''Limosilactobacillus.'' It is associated with active dental caries lesions. It is also commonly found in fermenting animal and plant material including s ...

'' and ''

Saccharomyces boulardii ''Saccharomyces boulardii'' is a tropical yeast first isolated from lychee and mangosteen peels in 1923 by French scientist Henri Boulard. Although early reports claimed distinct taxonomic, metabolic, and genetic properties, ''S. boulardii'' is ...

'' have been found to be ineffective. A combination of ''Lactobacillus plantarum'' and ''

Lactobacillus rhamnosus ''Lacticaseibacillus rhamnosus'' (previously ''Lactobacillus rhamnosus'') is a bacterium that originally was considered to be a subspecies of '' L. casei'', but genetic research found it to be a separate species in the ''L. casei'' clade, which ...

'' is effective in suppressing SIBO of abnormal gas producing organisms in the small intestine. A combination of probiotic strains has been found to produce better results than therapy with the antibiotic drug

. An elemental diet has been shown to be highly effective for eliminating SIBO with a two-week diet demonstrating 80% efficacy and a three-week diet demonstrating 85% efficacy. An elemental diet works via providing nutrition for the individual while depriving the bacteria of a food source. Additional treatment options include the use of

prokinetic A prokinetic agent (also prokineticin, gastroprokinetic agent, gastrokinetic agent or propulsive) is a type of drug which enhances gastrointestinal motility by increasing the frequency or strength of contractions, but without disrupting their rhyt ...

drugs such as 5-HT₄ receptor agonists or

motilin Motilin is a 22-amino acid polypeptide hormone in the motilin family that, in humans, is encoded by the ''MLN'' gene. Motilin is secreted by endocrine Mo cells (also referred to as M cells, which are not the same as the M cells, or microfold ...

agonists to extend the SIBO free period after treatment with an elemental diet or antibiotics. A diet void of certain foods that feed the bacteria can help alleviate the symptoms. For example, if the symptoms are caused by SIBO feeding on indigestible carbohydrate rich foods, following a

low-FODMAP diet A low-FODMAP diet is a person's global restriction of consumption of all fermentable carbohydrates ( FODMAPs), recommended only for a short time. A low-FODMAP diet is recommended for managing patients with irritable bowel syndrome (IBS) and can red ...

may help.

Epidemiology

According to breath testing, SIBO may be present in 34% of people with gastrointestinal symptoms. SIBO affects males and females in equal proportion. Race does not affect the risk of SIBO.

References

{{Irritable bowel syndrome Bacteria and humans Gastrointestinal tract disorders Syndromes affecting the gastrointestinal tract Steatorrhea-related diseases Gastrointestinal motility disorders