Small bowel bacterial overgrowth syndrome
Encyclopedia
Small bowel bacterial overgrowth syndrome (SBBOS), or small intestinal bacterial overgrowth (SIBO), also termed bacterial overgrowth; is a disorder of excessive bacterial growth in the small intestine
. Unlike the colon
(or large bowel), which is rich with bacteria
, the small bowel usually has less than 104 organisms per milliliter. Patients with bacterial overgrowth typically develop symptoms including nausea
, bloating
, vomiting
and diarrhea
, which is caused by a number of mechanisms. The diagnosis
of bacterial overgrowth is made by a number of techniques, with the gold standard
diagnosis being an aspirate
from the jejunum
that grows in excess of 105 bacteria
per millilitre. Risk factor
s for the development of bacterial overgrowth include the use of medications including proton pump inhibitors, anatomical
disturbances in the bowel, including fistula
e, diverticula and blind loops created after surgery, and resection of the ileo-cecal valve. Small bowel bacterial overgrowth syndrome is treated with antibiotic
s, which may be given in a cyclic fashion to prevent tolerance to the antibiotics.
s, many of which are also found in other conditions, making the diagnosis
challenging at times. Many of the symptoms are due to malabsorption
of nutrients due to the effects of bacteria which either metabolize nutrients or cause inflammation of the small bowel impairing absorption. The symptoms of bacterial overgrowth include nausea
, bloating
, flatus, chronic
diarrhea
, and constipation
. Some patients may develop abdominal discomfort and lose weight. Children with bacterial overgrowth may develop malnutrition
and have difficulty attaining proper growth
. Steatorrhea
is a sticky type of diarrhea, where lipid
s are malabsorbed and spill into the stool.
Patients with bacterial overgrowth that is longstanding can develop complications of their illness as a result of malabsorption of nutrients. Anemia
may occur from a variety of mechanisms, as many of the nutrients involved in production of red blood cell
s are absorbed in the affected small bowel. Iron
is absorbed in the more proximal parts of the small bowel, the duodenum
and jejunum
, 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
, and patients who malabsorb vitamin B12 can develop a megaloblastic anemia
with large red blood cells.
Certain species of bacteria are more commonly found in aspirates of the jejunum
taken from patients with bacterial overgrowth. The most common isolates are Escherichia coli
, Streptococcus
, Lactobacillus
, Bacteroides
, and Enterococcus
species.
Soon after birth, the gastrointestinal tract
is colonized with bacteria, which, on the basis of models with animals raised in a germ-free environment, have beneficial effects on function of the gastrointestinal tract. There are 500-1000 different species of bacteria that reside in the bowel. However, if the flora of the small bowel is altered, inflammation or altered digestion can occur, leading to symptoms. Many patients with chronic diarrhea have bacterial overgrowth as a cause or a contributor to their symptoms. While the consensus definition of chronic diarrhea varies, in general it is considered to be an alteration in stool consistency or increased frequency, that occurs for over three weeks. Various mechanisms are involved in the development of diarrhea in bacterial overgrowth. First, the excessive bacterial concentrations can cause direct inflammation of the small bowel cells, leading to an inflammatory diarrhea. The malabsorption of lipid
s, protein
s and carbohydrate
s may cause poorly digestible products to enter into the colon
. This can cause diarrhea by the osmotic drive
of these molecules, but can also stimulate the secretory mechanisms of colonic cells, leading to a secretory diarrhea.
or movement of the small bowel or anatomical changes that lead to stasis
, (2) disorders in the immune system
and (3) conditions that cause more bacteria from the colon
to enter the small bowel.
Problems with motility may either be diffuse, or localized to particular areas. Diseases like scleroderma
and possibly celiac disease 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 diverticula that can cause bacteria to accumulate. After surgery involving the stomach
and duodenum
(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.
Disorders of the immune system can cause bacterial overgrowth. Chronic pancreatitis
, or inflammation of the pancreas
can cause bacterial overgrowth through mechanisms linked to this. The use of immunosuppressant
medications to treat other conditions can cause this, as evidenced from animal models. Other causes include inherited immunodeficiency conditions, such as combined variable immunodeficiency, IgA deficiency, and hypogammaglobulinemia
.
Finally, abnormal connections between the bacteria
-rich colon and the small bowel can increase the bacterial load in the small bowel. Patients with Crohn's disease
or other diseases of the ileum
may require surgery that removes the ileocecal valve
connecting the small and large bowel; this leads to an increased reflux of bacteria into the small bowel. After bariatric surgery
for obesity, connections between the stomach and the ileum
can be formed, which may increase bacterial load in the small bowel. Proton pump inhibitor
medications that decrease acid in the stomach
cause bacterial overgrowth by a similar mechanism, as they prevent the anti-bacterial effects of acid in the stomach. The clinical significance of this in causing symptoms is unclear.
The diagnosis of bacterial overgrowth can be made by physicians in various ways. Malabsorption
can be detected by a test called the D-xylose test. Xylose
is a sugar that does not require enzymes to be digested. The D-xylose test involves having a patient to drink a certain quantity of D-xylose, and measuring levels in the urine
and blood
; if there is no evidence of D-xylose in the urine
and blood
, it suggests that the small bowel is not absorbing properly (as opposed to problems with enzymes required for digestion).
The gold standard for detection of bacterial overgrowth is the aspiration of more than 105 bacteria per millilitre from the small bowel. The normal small bowel has less than 104 bacteria per millilitre.
Breath tests have been developed to test for bacterial overgrowth, based on bacterial metabolism of carbohydrates to hydrogen
, or based on the detection of by-products of digestion of carbohydrates that are not usually metabolized. The hydrogen breath test
involves giving patients a load of carbohydrate (usually in the form of rice
) and measuring expired hydrogen concentrations after a certain time. It compares well to jejunal aspirates in making the diagnosis of bacterial overgrowth. 13C and 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 breath test involves the administration of the bile acid 14C glychocholic acid, and the detection of 14CO2, which would be elevated in bacterial overgrowth.
Some patients with symptoms of bacterial overgrowth will undergo gastroscopy, or visualization of the stomach and duodenum with an endoscopic camera
. Biopsies of the small bowel in bacterial overgrowth can mimic those of celiac disease, making the diagnosis more challenging. Findings include blunting of villi, hyperplasia of crypts and an increased number of lymphocyte
s in the lamina propria
.
However, some physicians suggest that if the suspicion of bacterial overgrowth is high enough, the best diagnostic test is a trial of treatment. If the symptoms improve, an empiric diagnosis of bacterial overgrowth can be made.
, rifaximin, amoxicillin-clavulanate, fluoroquinolone antibiotics and tetracycline have been used; however, the best evidence is for the use of norfloxacin
and amoxicillin-clavulanate.
A course of one week of antibiotics is usually sufficient to treat the condition. However, if the condition recurs, antibiotics can be given in a cyclical fashion in order 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.
The condition that predisposed the patient to bacterial overgrowth should also be treated. For example, if the bacterial overgrowth is caused by chronic pancreatitis
, the patient should be treated with coated pancreatic enzyme
supplements.
Probiotic
s are bacterial preparations that alter the bacterial flora in the bowel to cause a beneficial effect. Their role in bacterial overgrowth is somewhat uncertain.
A diet void of certain foods that feed the bacteria can help alleviate the symptoms.
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
. Unlike the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
(or large bowel), which is rich with bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, the small bowel usually has less than 104 organisms per milliliter. Patients with bacterial overgrowth typically develop symptoms including nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, bloating
Bloating
Bloating is any abnormal general swelling, or increase in diameter of the abdominal area. As a symptom, the patient feels a full and tight abdomen, which may cause abdominal pain sometimes accompanied by increased borborygmus or more seriously the total lack of borborygmus.-Symptoms:The most common...
, vomiting
Vomiting
Vomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
and diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
, which is caused by a number of mechanisms. The diagnosis
Medical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...
of bacterial overgrowth is made by a number of techniques, with the gold standard
Gold standard (test)
In medicine and statistics, gold standard test refers to a diagnostic test or benchmark that is the best available under reasonable conditions. It does not have to be necessarily the best possible test for the condition in absolute terms...
diagnosis being an aspirate
Needle aspiration biopsy
Needle aspiration biopsy , may refer to fine needle aspiration cytology , fine needle aspiration biopsy and fine needle aspiration , is a diagnostic procedure sometimes used to investigate superficial lumps or masses...
from the jejunum
Jejunum
The jejunum is the middle 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 middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
that grows in excess of 105 bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
per millilitre. Risk factor
Risk factor
In epidemiology, a risk factor is a variable associated with an increased risk of disease or infection. Sometimes, determinant is also used, being a variable associated with either increased or decreased risk.-Correlation vs causation:...
s for the development of bacterial overgrowth include the use of medications including proton pump inhibitors, anatomical
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
disturbances in the bowel, including fistula
Fistula
In medicine, a fistula is an abnormal connection or passageway between two epithelium-lined organs or vessels that normally do not connect. It is generally a disease condition, but a fistula may be surgically created for therapeutic reasons.-Locations:Fistulas can develop in various parts of the...
e, diverticula and blind loops created after surgery, and resection of the ileo-cecal valve. Small bowel bacterial overgrowth syndrome is treated with antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
s, which may be given in a cyclic fashion to prevent tolerance to the antibiotics.
Clinical presentation
Bacterial overgrowth can cause a variety of symptomSymptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
s, many of which are also found in other conditions, making the diagnosis
Medical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...
challenging at times. Many of the symptoms are due to malabsorption
Malabsorption
Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal tract.Impairment can be of single or multiple nutrients depending on the abnormality...
of nutrients due to the effects of bacteria which either metabolize nutrients or cause inflammation of the small bowel impairing absorption. The symptoms of bacterial overgrowth include nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, bloating
Bloating
Bloating is any abnormal general swelling, or increase in diameter of the abdominal area. As a symptom, the patient feels a full and tight abdomen, which may cause abdominal pain sometimes accompanied by increased borborygmus or more seriously the total lack of borborygmus.-Symptoms:The most common...
, flatus, chronic
Chronic (medicine)
A chronic disease is a disease or other human health condition that is persistent or long-lasting in nature. The term chronic is usually applied when the course of the disease lasts for more than three months. Common chronic diseases include asthma, cancer, diabetes and HIV/AIDS.In medicine, the...
diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
, and constipation
Constipation
Constipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation...
. Some patients may develop abdominal discomfort and lose weight. Children with bacterial overgrowth may develop malnutrition
Malnutrition
Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
and have difficulty attaining proper growth
Failure to thrive
Failure to thrive is a medical term which is used in both pediatric and adult human medicine, as well as veterinary medicine ....
. Steatorrhea
Steatorrhea
Steatorrhea is the presence of excess fat in feces. Stools may also float due to excess lipid, have an oily appearance and be especially foul-smelling. An oily anal leakage or some level of fecal incontinence may occur. There is increased fat excretion, which can be measured by determining the...
is a sticky type of diarrhea, where lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
s are malabsorbed and spill into the stool.
Patients with bacterial overgrowth that is longstanding can develop complications of their illness as a result of malabsorption of nutrients. Anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
may occur from a variety of mechanisms, as many of the nutrients involved in production of red blood cell
Red blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s are absorbed in the affected small bowel. Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
is absorbed in the more proximal parts of the small bowel, the duodenum
Duodenum
The duodenum is the first 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 anterior intestine or proximal intestine may be used instead of duodenum...
and jejunum
Jejunum
The jejunum is the middle 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 middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
, and patients with malabsorption of iron can develop a microcytic anemia
Microcytic anemia
Microcytic anemia is a generic term for any type of anemia characterized by small red blood cells. The normal mean corpuscular volume is 76-100 fL, with smaller cells as macrocytic....
, with small red blood cells. Vitamin B12
Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
is absorbed in the last part of the small bowel, the ileum
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 be used instead of ileum.The ileum follows the duodenum...
, and patients who malabsorb vitamin B12 can develop a megaloblastic anemia
Megaloblastic anemia
Megaloblastic anemia is an anemia that results from inhibition of DNA synthesis in red blood cell production. When DNA synthesis is impaired, the cell cycle cannot progress from the G2 growth stage to the mitosis stage...
with large red blood cells.
Pathophysiology
Jejunum
The jejunum is the middle 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 middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
taken from patients with bacterial overgrowth. The most common isolates are Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
, Streptococcus
Streptococcus
Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...
, Lactobacillus
Lactobacillus
Lactobacillus is a genus of Gram-positive facultative anaerobic or microaerophilic rod-shaped bacteria. They are a major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid. They are common and usually benign...
, Bacteroides
Bacteroides
Bacteroides is a genus of Gram-negative, bacillus bacteria. Bacteroides species are non-endospore-forming, anaerobes, and may be either motile or non-motile, depending on the species. The DNA base composition is 40-48% GC. Unusual in bacterial organisms, Bacteroides membranes contain sphingolipids...
, and Enterococcus
Enterococcus
Enterococcus is a genus of lactic acid bacteria of the phylum Firmicutes. Enterococci are Gram-positive cocci that often occur in pairs or short chains, and are difficult to distinguish from streptococci on physical characteristics alone. Two species are common commensal organisms in the...
species.
Soon after birth, the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
is colonized with bacteria, which, on the basis of models with animals raised in a germ-free environment, have beneficial effects on function of the gastrointestinal tract. There are 500-1000 different species of bacteria that reside in the bowel. However, if the flora of the small bowel is altered, inflammation or altered digestion can occur, leading to symptoms. Many patients with chronic diarrhea have bacterial overgrowth as a cause or a contributor to their symptoms. While the consensus definition of chronic diarrhea varies, in general it is considered to be an alteration in stool consistency or increased frequency, that occurs for over three weeks. Various mechanisms are involved in the development of diarrhea in bacterial overgrowth. First, the excessive bacterial concentrations can cause direct inflammation of the small bowel cells, leading to an inflammatory diarrhea. The malabsorption of lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
s, protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s and carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
s may cause poorly digestible products to enter into the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
. This can cause diarrhea by the osmotic drive
Osmosis
Osmosis is the movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, aiming to equalize the solute concentrations on the two sides...
of these molecules, but can also stimulate the secretory mechanisms of colonic cells, leading to a secretory diarrhea.
Risk factors and causes
Certain patients are more predisposed to the development of bacterial overgrowth because of certain risk factors. These factors can be grouped into three categories: (1) disordered motilityMotility
Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in...
or movement of the small bowel or anatomical changes that lead to stasis
Stasis (medicine)
In medicine, stasis is the state in which the normal flow of a body liquid stops, for example the flow of blood through vessels or of intestinal contents through the digestive tract....
, (2) disorders in the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
and (3) conditions that cause more bacteria from the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
to enter the small bowel.
Problems with motility may either be diffuse, or localized to particular areas. Diseases like scleroderma
Scleroderma
Systemic sclerosis or systemic scleroderma is a systemic autoimmune disease or systemic connective tissue disease that is a subtype of scleroderma.-Skin symptoms:...
and possibly celiac disease 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 diverticula that can cause bacteria to accumulate. After surgery involving the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
and duodenum
Duodenum
The duodenum is the first 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 anterior intestine or proximal intestine may be used instead of duodenum...
(most commonly with Billroth II
Billroth II
Billroth II, more formally Billroth's operation II, is an operation in which the greater curvature of the stomach is connected to the first part of the jejunum in a side-to-side manner. This often follows resection of the lower part of the stomach . The antrectomy is not part of the orignially...
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.
Disorders of the immune system can cause bacterial overgrowth. Chronic pancreatitis
Pancreatitis
Pancreatitis is inflammation of the pancreas. It occurs when pancreatic enzymes that digest food are activated in the pancreas instead of the small intestine. It may be acute – beginning suddenly and lasting a few days, or chronic – occurring over many years...
, or inflammation of the pancreas
Pancreas
The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
can cause bacterial overgrowth through mechanisms linked to this. The use of immunosuppressant
Immunosuppressant
An immunosuppressant is any substance that performs immunosuppression of the immune system. They may be either exogenous, as immunosuppressive drugs, or endogenous, as ,e. g., testosterone...
medications to treat other conditions can cause this, as evidenced from animal models. Other causes include inherited immunodeficiency conditions, such as combined variable immunodeficiency, IgA deficiency, and hypogammaglobulinemia
Hypogammaglobulinemia
Hypogammaglobulinemia is a type of immune disorder characterized by a reduction in all types of gamma globulins.Hypogammaglobulinemia is a characteristic of common variable immunodeficiency.-Terminology:...
.
Finally, abnormal connections between the bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
-rich colon and the small bowel can increase the bacterial load in the small bowel. Patients with Crohn's disease
Crohn's disease
Crohn's disease, also known as regional enteritis, is a type of inflammatory bowel disease that may affect any part of the gastrointestinal tract from mouth to anus, causing a wide variety of symptoms...
or other diseases of the ileum
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 be used instead of ileum.The ileum follows the duodenum...
may require surgery that removes the ileocecal valve
Ileocecal valve
The ileocecal valve, or ileocaecal valve, is of a bilabial papilla structure with physiological sphincter muscle situated at the junction of the small intestine and the large intestine, with recent evidence indicating an anatomical sphincter may also be present in humans) Its critical function is...
connecting the small and large bowel; this leads to an increased reflux of bacteria into the small bowel. After bariatric surgery
Bariatric surgery
Bariatric surgery includes a variety of procedures performed on people who are obese. Weight loss is achieved by reducing the size of the stomach with an implanted medical device or through removal of a portion of the stomach or by resecting and re-routing the small intestines...
for obesity, connections between the stomach and the ileum
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 be used instead of ileum.The ileum follows the duodenum...
can be formed, which may increase bacterial load in the small bowel. Proton pump inhibitor
Proton pump inhibitor
Proton-pump inhibitors are a group of drugs whose main action is a pronounced and long-lasting reduction of gastric acid production. They are the most potent inhibitors of acid secretion available today. The group followed and has largely superseded another group of pharmaceuticals with similar...
medications that decrease acid in the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
cause bacterial overgrowth by a similar mechanism, as they prevent the anti-bacterial effects of acid in the stomach. The clinical significance of this in causing symptoms is unclear.
Diagnosis
Malabsorption
Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal tract.Impairment can be of single or multiple nutrients depending on the abnormality...
can be detected by a test called the D-xylose test. Xylose
Xylose
Xylose 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 the precursor to hemicellulose, one of the main constituents of biomass...
is a sugar that does not require enzymes to be digested. The D-xylose test involves having a patient to drink a certain quantity of D-xylose, and measuring levels in the urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
and blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
; if there is no evidence of D-xylose in the urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
and blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
, it suggests that the small bowel is not absorbing properly (as opposed to problems with enzymes required for digestion).
The gold standard for detection of bacterial overgrowth is the aspiration of more than 105 bacteria per millilitre from the small bowel. The normal small bowel has less than 104 bacteria per millilitre.
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, or based on the detection of by-products of digestion of carbohydrates that are not usually metabolized. The hydrogen breath test
Hydrogen Breath Test
A hydrogen breath test is used as a clinical medical diagnosis for people with irritable bowel syndrome, and common food intolerances. The test is simple, non-invasive, and is performed after a short period of fasting . Even though the test is normally known as a "Hydrogen Breath Test" some...
involves giving patients a load of carbohydrate (usually in the form of rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
) and measuring expired hydrogen concentrations after a certain time. It compares well to jejunal aspirates in making the diagnosis of bacterial overgrowth. 13C and 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 breath test involves the administration of the bile acid 14C glychocholic acid, and the detection of 14CO2, which would be elevated in bacterial overgrowth.
Some patients with symptoms of bacterial overgrowth will undergo gastroscopy, or visualization of the stomach and duodenum with an endoscopic camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
. Biopsies of the small bowel in bacterial overgrowth can mimic those of celiac disease, making the diagnosis more challenging. Findings include blunting of villi, hyperplasia of crypts and an increased number of lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s in the lamina propria
Lamina propria
The lamina propria is a constituent of the moist linings known as mucous membranes or mucosa, which line various tubes in the body ....
.
However, some physicians suggest that if the suspicion of bacterial overgrowth is high enough, the best diagnostic test is a trial of treatment. If the symptoms improve, an empiric diagnosis of bacterial overgrowth can be made.
Treatment
Bacterial overgrowth is usually treated with a course of antibiotics. A variety of antibiotics, including neomycinNeomycin
Neomycin is an aminoglycoside antibiotic that is found in many topical medications such as creams, ointments, and eyedrops. The discovery of Neomycin dates back to 1949. It was discovered in the lab of Selman Waksman, who was later awarded the Nobel Prize in Physiology and medicine in 1951...
, rifaximin, amoxicillin-clavulanate, fluoroquinolone antibiotics and tetracycline have been used; however, the best evidence is for the use of norfloxacin
Norfloxacin
Norfloxacin is a synthetic chemotherapeutic antibacterial agent occasionally used to treat common as well as complicated urinary tract infections. It is sold under various brand names with the most common being Noroxin. In form of ophthalmic solutions it is known as Chibroxin...
and amoxicillin-clavulanate.
A course of one week of antibiotics is usually sufficient to treat the condition. However, if the condition recurs, antibiotics can be given in a cyclical fashion in order 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.
The condition that predisposed the patient to bacterial overgrowth should also be treated. For example, if the bacterial overgrowth is caused by chronic pancreatitis
Chronic pancreatitis
Chronic pancreatitis is a long-standing inflammation of the pancreas that alters its normal structure and functions. It can present as episodes of acute inflammation in a previously injured pancreas, or as chronic damage with persistent pain or malabsorption....
, the patient should be treated with coated pancreatic enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
supplements.
Probiotic
Probiotic
Probiotics are live microorganisms thought to be beneficial to the host organism. According to the currently adopted definition by FAO/WHO, probiotics are: "Live microorganisms which when administered in adequate amounts confer a health benefit on the host"...
s are bacterial preparations that alter the bacterial flora in the bowel to cause a beneficial effect. Their role in bacterial overgrowth is somewhat uncertain.
A diet void of certain foods that feed the bacteria can help alleviate the symptoms.