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Intestinal bacterial overgrowth
- 1. INTESTINAL FUNCTION TEST (BACTERIAL OVER GROWTH ) Abdulla ek 3rd SEM MSC MLT
- 2. BACTERIAL OVERGROWTH ο The proximal small intestine (duodenum and jejunum) normally contains few bacteria. ο Most ingested bacteria do not survive the acidic environment of the stomach and therefore few live organisms normally enter the small bowel. ο The motility of the jejunum prevents fecal-type organisms from progressing up into the jejunum from the cecum. ο The ileum normally contains some fecal-type bacteria.
- 3. BACTERIAL OVERGROWTH ο Colonization of the upper small bowel is described as bacterial overgrowth ο and usually occurs as a consequence of other abnormalities (structural or motility disorders) of the small intestine
- 4. PATHOGENESIS ο Defense against SIBO β Gastric acid β Intestinal motility β Intact ileo-cecal valve β Immunoglobulin's β Bacteriostatic properties of pancreatic and biliary secretion
- 5. PATHOGENESIS ο Causes β Achlorhydria β Motility disorder eg.scleroderma β Anatomical defects eg. fistula, resection, strictures β Immune deficiencies β Pancreatic exocrine deficiency
- 6. COMPLICATIONS ο The bacteria colonizing the small bowel (such as Escherichia coli) deconjugate and dehydroxylate bile salts, leading to conjugated bile salt deficiency, which causes fat malabsorption. ο Bacterial metabolism of vitamin B, may also occur, leading to vitamin B deficiency
- 7. CLINICAL SYMPTOMS ο abdominal pain ο Diarrhea ο steatorrhea.
- 8. DIAGNOSIS Gold standard method ο Small-bowel aspiration for quantitative culture traditionally has been regarded as the gold standard for the diagnosis of SIBO. ο Because it is imperative not to contaminate the sample. ο aspiration is performed either through an endoscopically or fluoroscopically.
- 9. ο Limitations ο Cost. ο Invasive nature. ο Time commitment, ο Lack of adequate validation. ο Accuracy of culturing. ο the potential for missing distal small-bowel bacterial overgrowth.
- 10. BREATH TESTING ο readily available. ο Safe. ο inexpensive. ο noninvasive ο alternative to jejunal aspiration culture for the diagnosis of SIBO.
- 11. PRINCIPLE OF BREATH TEST ο By measuring exhaled gases produced by bacterial fermentation of various orally ingested substrates, the bacterial load within the small bowel can be assessed indirectly. ο The measured gases can include labeled carbon dioxide (CO2), hydrogen, and methane.
- 12. ο For the labeled CO2 studies, the orally ingested substrates include ο 14C-glycocholate ο 13C-glycocholate ο 14C-xylose, ο 13C-xylose ο hydrogen and methane breath testing, the substrates include ο glucose ο lactulose
- 13. CARBON DIOXIDE BREATH TESTING ο Testing used either the radioactive isotope of carbon, 14C or the nonradioactive 13C isotope. ο Limitations ο One of the greatest challenges with CO2 breath testing was correcting for the endogenous CO2 production ο which differed considerably in the various disease states adversely affecting test accuracy. ο Furthermore, the process of conjugating substrates with labeled carbon added to the cost and limited availability. ο For these reasons, CO2 breath testing has been abandoned in clinical practice.
- 14. 14C-GLYCOCHOLATE BREATH TEST ο The principle underlying the use of glycocholic acid was that ο under normal circumstances, bile acids readily were absorbed in the ileum. ο Any unabsorbed glycocholic acid was subject to metabolism, either by bacteria in the proximal small bowel before ileal absorption, or in the colon in the event of glycocholate malabsorption.
- 15. ο When there is bacterial overgrowth,the bacteria deconjugate the glycocholic acid to produce 14C-glycine that is absorbed and metabolized with an increase in breath I4CO2. ο A subsequent increase in labeled CO2 in expired breath within 6 hours was interpreted as a positive study.
- 16. LIMITATIONS ο inability to distinguish small bowel from colonic bacterial deconjugation of the glycocholic acid ο decreased accuracy with underlying rapid small-bowel transit. ο A compounding concern is the theoretical risk of long-term radiation exposure with the 14C-labeled substrates
- 17. 13C/14C D-XYLOSE ο D-xylose is a poorly absorbed 5-carbon monosaccharide found in plants. ο D-xylose labeled with either 13C or 14C was ingested orally, and metabolized by gut bacteria yielding labeled CO2 measured in the breath. ο However, D-xylose is variably absorbed and metabolized, ο which can blur the baseline breath CO2 measurements, ο making it more difficult to measure labeled CO2 production in the setting of SIBO.
- 18. ο Limitations ο D-xylose may be a poor metabolic substrate for common coliform bacteria including Escherichia coli, enterococci, and clostridia. ο thereby increasing the risk of false-negative results.
- 19. HYDROGEN AND METHANE BREATH TESTING ο Patient Preparation ο Avoidance of wheat-based foods and fiber for 12 hours before. ο Fasting breath hydrogen is typically <5 ppm (5 pL1L) and concentrations 20 ppm (20 pL/L) may be an indication of malabsorption or bacterial overgrowth.'" ο Oral hygiene before ingestion of the substrate in hydrogen breath tests minimizes the production of hydrogen by oral bacteria.
- 20. ο Brushing of teeth or use of an antibacterial mouthwash (e.g., 1% chlorhexidine) is recommended.'" ο Mouthwash containing alcohol should not be used, because this may interfere in the measurement of hydrogen. ο Cigarette smolie contains high hydrogen levels and smoking is therefore not permitted immediately before or during the test.
- 21. ο Hydrogen breath testing was introduced as an alternative to CO2 breath testing for SIBO. ο Hydrogen breath testing is based on the principle that bacterial metabolism (fermentation) of nonabsorbed carbohydrates is the sole source of hydrogen and methane in exhaled breath. ο ource of hydrogen and methane in exhaled breath. After the oral ingestion of various substrates, hydrogen can be measured in exhaled breath using gas chromatography and reported as a concentration in parts per million (ppm).
- 22. ο Methane can be measured in a similar manner to hydrogen.
- 23. LACTULOSE BREATH TEST ο Lactulose (usually given in a dose of 10 g in 200 mL water) is a nonabsorbahle disaccharide. ο In a normal subject, breath hydrogen does not increase until the lactulose enters the large intestine; the time from ingestion to a rise in breath hydrogen is therefore normally an indication of small bowel transit time.
- 24. ο In bacterial overgrowth, there is an early rise in breath hydrogen of at least 20 ppm within 30 minutes of ingestion of lactulose. ο The early increase is diagnostic when it can be distinguished clearly from the later colonic rise. Frequent measurements (e.g., at 5- minute intervals) are essential in the first 30 minutes, with measurements every 15 minutes thereafter for up to 3 hours.
- 25. GLUCOSE BREATH TEST ο Glucose is a monosaccharide that is completely absorbed in the proximal small intestine under normal physiologic conditions. ο However, in the presence of SIBO, glucose is fermented by bacteria before it can be absorbed in the proximal intestine. ο an individual with SIBO, the proximally displaced bacteria theoretically should lead to the fermentation of glucose and a resultant increase in breath hydrogen excretion.
- 26. ο 50 g glucose dose in 250 mL of water, with breath samples collected every 15 minutes for a total of 120 minutes, and a positive test defined as an increase in hydrogen levels by 12 ppm or more from baseline. ο In bacterial overgrowth, breath hydrogen usually increases within 75 minutes of ingestion of glucose and sometimes within 30 minutes.
- 27. ο The finding of an increased fasting breath hydrogen has high specificity for bacterial overgrowth but poor sensitivity. ο however, a fasting breath hydrogen >15 ppm and an increment of at least 12 ppm within 2 hours of a 50 g glucose challenge is diagnostic of bacterial over growth.
- 28. ο Limitation ο Variations in gastric emptying rate and small bowel transit times are problems that livnit the diagnostic accuracy of the breath hydrogen tests.
- 30. Reference ο Teatz text book of clinical bio chemistry (4 th edition ) ο Richard J. Saad and William D. Chey. Breath Testing for Small Intestinal Bacterial Overgrowth: Maximizing Test Accuracy 2014;12. (https://sibotesting.com/wp- content/uploads/2015/10/SIBO-Testing- Article.pdf )