Small Intestinal Bacterial Overgrowth Flashcards
SIBO
SIBO by performing- ing small intestine aspirates (primarily jejunal and duodenal) and culturing the fluid.
SIBO was then defined as the presence of bacteria in the proximal small intestine of greater than 1 × 105 colony forming units (cfu)/mL
Diagnosed
SIBO can be diagnosed as the presence of excess bacteria (either quantitative [>105 cfu/mL] or qualitative [excess bacteria of colonic origin] in the small intestine accompanied by intestinal or extra-intestinal symptoms thought to result from this excess.
The bacterial content of the small intestine is drastically lower than that of the colon for 3 major reasons:
1) gastric acid prevents bacterial overgrowth in the stom- ach and proximal small intestine; (2) normal fasting intesti- nal motor activity (i.e., migrating motor complex) prevents accumulation of bacteria within the small intestine; (3) the ileocecal valve limits reflux of colonic bacteria into the dis- tal small intestine.
Mucosal injury induced by bacteria and/or their toxins or metabolic products
Loss of brush-border enzymes
Injury to epithelial barrier leading to enhanced intestinal permeability
Inflammatory response generating inflammatory cytokines
Loss of brush-border enzymes
Injury to epithelial barrier leading to enhanced intestinal permeability
Inflammatory response generating inflammatory cytokines
Carbohydrate maldigestion and malabsorption
Protein-losing enteropathy; bacterial translocation and portal and systemic endotoxemia
Liver injury and inflammation, systemic inflammatory responses
Luminal competition with the host for nutrients
Consumption of dietary protein
Consumption of vitamin B12; production of cobamides Consumption of thiamine
Consumption of nicotinamide
Consumption of dietary protein
Consumption of vitamin B12; production of cobamides Consumption of thiamine
Consumption of nicotinamide
Hypoproteinemia, edema
B12 deficiency, megaloblastic anemia, neurologic symptoms Thiamine deficiency
Nicotinamide deficiency
Bacterial metabolism
Fermentation of unabsorbed carbohydrates Deconjugation of primary bile acids Synthesis of vitamin K Synthesis of folate Synthesis of d-lactic acid Synthesis of alcohol Synthesis of acetaldehyde
Fermentation of unabsorbed carbohydrates Deconjugation of primary bile acids Synthesis of vitamin K Synthesis of folate Synthesis of d-lactic acid Synthesis of alcohol Synthesis of acetaldehyde
Bloating, distension, flatulence; auto-brewery syndrome Diarrhea due to the effects of deconjugated bile acids in the
colon; depletion of the bile acid pool leading to fat and fat- soluble vitamin malabsorption
Interference with dosing of vitamin K antagonists (e.g., warfarin)
High serum folate levels
d-lactic acidosis
Liver injury, auto-brewery syndrome
Liver injury
The “gold standard” test for SIBO
quantitative culture of a jejunal aspirate.
direct aspiration of fluid during endoscopy is the most common method used,
The traditional cut-off level diagnostic of SIBO
The traditional cut-off level diagnostic of SIBO is ≥105 cfu/mL of aerobic Gram-negative or strict anaerobic bacteria obtained from a jejunal aspirate
Indirect Test
Breath testing is cur- rently the most common indirect test used because it is noninva- sive, relatively inexpensive, and simple to perform.
The first breath test developed for the diagnosis of SIBO was the bile acid breath test.97 In this test, bile acids are radiolabeled with 14C or 13C and, when deconjugated by bacteria, the radio- labeled CO2 is released, absorbed, and excreted in the breath.
Breath test
The most commonly used SIBO breath tests today measure expired hydrogen and methane following the ingestion of a sugar substrate.
Most common sugar substrate
Glucose and lactulose are the most common sugar substrates used in hydrogen-based breath testing.
Sugar
Glucose is a monosaccha- ride that is absorbed primarily in the proximal small intestine, whereas lactulose is a synthetic nonabsorbable disaccharide that undergoes fermentation in the colon
Before and after ingestion of the carbohydrate substrate, patients are asked to exhale into a tube that is connected to a sam- pling bag and syringe to obtain baseline and sequential hydrogen and methane values.
The Rome consensus group recommends 50 g of glucose in 250 mL of water with breath samples collected every 15 to 20 minutes for a total of 120 to 180 minutes, whereas the North American consensus group recommends use of 75 g of glucose in 1 cup of water and a total testing period of 120 min- utes
An increase in breath hydrogen after oral administration of glucose is diagnostic of SIBO although the absolute level of increase diagnostic of SIBO remains somewhat controversial.
hydrogen increase ≥20 parts per million (ppm) over baseline and sustained over at least 2 time points within 90 minutes is recom- mended by the North American consensus group; an increase >10 to 12 ppm from baseline also has been suggested.
Tc scintigraphy,
Tc scintigraphy, the time of increase in breath hydrogen levels corresponded with an increase in accumulation of 99m Tc in the cecum in 88% of cases, suggesting that a positive breath test results from colonic bacteria metabolizing lactulose and not as a result of SIBO129; similar results have been found by others
Cut off
The North American consensus group recommends that an increase in breath methane of ≥10 ppm be used as an addi- tional criterion to diagnose SIBO.
Cholyl-PABA,
a synthetic compound created by conjugat- ing cholic acid with para-aminobenzoic acid (PABA), is catabo- lized by bacterial hydrolase to release free PABA, which can then be detected in the urine.
PABA provides a simple noninvasive method for detecting SIBO but is unable to distinguish between SIBO and other causes of malabsorption with any degree of reli- ability and never garnered widespread clinical use
indirect test for SIBO.
Urinary indican (indoxyl sulfate, a by-product of intestinal bacterial metabolism of tryptophan) levels also have been used as an indirect test for SIBO.
TREATMENT
There are 3 components to the treatment of SIBO: (1) correcting the underlying potentially causative disease; (2) addressing any associated nutritional deficiencies; and (3) modifying the altered microbiota.
The primary goal should be the treatment or cor- rection of any potentially causative underlying disease or defect when possible.
Oral Antibiotic Regimens Used to Treat SIBO
At present, oral antibiotics are the mainstay of therapy for SIBO.
Amoxicillin-Clavulanate 500/125 mg 2 or 3 times daily Ciprofloxacin 250-500 mg twice daily Doxycycline 100 mg twice daily Metronidazole 500 mg twice daily Neomycin 500 mg 2 or 3 times daily Norfloxacin 400 mg twice daily Rifaximin 400-550 mg 2 or 3 times daily Tetracycline 250-500 mg 4 times each day Trimethoprim/Sulfamethoxazole 160/800 mg twice daily
