The Pathogenesis of Gastrointestinal Bacterial Overgrowth

Abstract

The normal indigenous intestinal microflora consists of about 10¹⁵ bacteria that under physiological conditions reside mainly in the lower gastrointestinal tract. Bacterial overgrowth implies abnormal bacterial colonization of the upper gut, resulting from failure of specific defense mechanisms restricting colonization under physiological conditions. At present two types of bacterial overgrowth with defined pathogenesis can be distinguished: (1) gastric overgrowth with upper respiratory tract microflora resulting from selective failure of the gastric acid barrier, and (2) gastrointestinal overgrowth with Gram-negative bacilli (enteric bacteria) resulting from failure of intestinal clearance. Helicobacter pylori-induced gastritis of the oxyntic mucosa is the main cause of acquired failure of the gastric acid barrier, which is common among the healthy elderly. Intestinal clearance may fail as the result of impaired intestinal peristalsis or anatomical abnormalities that alter luminal flow. Impaired peristalsis is associated with conditions interfering with intestinal neuromuscular function including myopathic, neuropathic, autoimmune, infectious, inflammatory, metabolic, endocrine, and neoplastic diseases. Anatomical abnormalities are mainly the result of gastrointestinal surgery, intestinal diverticula or fistula. Combined failure of intestinal clearance and the gastric acid barrier results in more severe colonization with Gram-negative bacilli. Gram-negative bacilli are uncommon in the upper gut of otherwise healthy individuals with gastric hypochlorhydria, being acquired (H. pylori) or drug-induced. Significant bacterial overgrowth with Gram-negative bacilli is a rational in the search for an explanation to optimize clinical management. The clinical significance of colonization with upper respiratory tract microflora remains unclear. Translocation of live bacteria, their metabolic products, or antigens from a small bowel colonized by Gram-negative bacilli play a role in the pathogenesis of spontaneous bacterial peritonitis in hepatic disease and in certain types of sepsis, indicating that further studies can point to new patient populations with potential benefit from medical treatment.

Prevalence and clinical significance of small intestinal bacterial overgrowth in patients with chronic liver disease

“…Gastric acidity, anatomical integrity of the digestive tract, peristaltic activity of the bowel, immunglobulin A plays a major role in maintaining the balance between the intestinal microflora and host mechanisms fails bacterial over studies, small intestinal bacterial over growth (SIBO) is defined as the microbiological presence of more than10 colony forming units (CFU) per ml of Various studies showed the relationship between the derangement of gut flora and increased prevalence of SIBO in cirrhotic patients. 5,6 Decrease in small bowel motility and increasein adrenergic activity in cirrhotic patients may lead bacterial overgrowth. [5][6][7] In addition to the range of symptoms and consequences of SIBO per se, increasing evidence suggests tha of intestinal flora is of substantial clinical relevance to Institute of Medical Gastroenterology, Madras Medical College and Rajiv Gandhi Government General Hospital, Chennai,…”

“…5,6 Decrease in small bowel motility and increasein adrenergic activity in cirrhotic patients may lead bacterial overgrowth. [5][6][7] In addition to the range of symptoms and consequences of SIBO per se, increasing evidence suggests tha of intestinal flora is of substantial clinical relevance to Institute of Medical Gastroenterology, Madras Medical College and Rajiv Gandhi Government General Hospital, Chennai,…”

Increased Gut Permeability and Microbiota Change Associate with Mesenteric Fat Infl ammation and Metabolic Dysfunction in Diet-Induced Obese Mice

“…Due to the bactericidal properties of the gastric and also bile acids, the stomach and proximal small intestine contain only few microorganisms. Patients with reduced gastric acid levels (achlorhydria or hypochlorhydria for example) may suffer from bacterial overgrowth and subsequent inflammatory or malignant complications (Friis-Hansen, 2006;Husebye, 2005;Naylor & Axon, 2003). With increasing distance from the stomach and…”

Potentials and Limitations of Bile Acids and Probiotics in Diabetes Mellitus

“…Diabetes is a disease that incorporates various metabolic disturbances such as impaired glucose haemostasis, blood dyscrasias and hyperlipidemia. Major disturbances also include slower gut movement (gastroparesis) and microfloral overgrowth (especially of fermentation bacteria and yeasts due to the slightly more acidic gut contents) Husebye 2005). Improving diabetes complications, reducing prevalence and restoring normal physiological patterns should significantly optimise diabetes treatment and the quality of life for diabetic patients.…”