Until recently, little attention has been given to the bacterial population of the upper gastrointestinal (GI) tract. This neglect was partly due to the relative inaccessibility of this region of the alimentary tract for study, and the limitations of culture methods to detect a flora that was normally not numerous and mostly anaerobic. With recent technical advances in microbiology, however, the microflora of the small intestine has been extensively investigated, with the complex effects of bacteria in health and disease states becoming better recognized. Growth of unusually large numbers of bacteria in the small bowel has been identified in certain diseases to be associated with severe metabolic consequences, most notably steatorrhea, diarrhea, anemia, and weight loss. The mechanisms of these profound effects are the subject of this review.
NORMAL MICROFLORA OF THE SMALL INTESTINE
The human GI tract is normally sterile at birth and gradually becomes colonized with Escherichia coli
Drude RB, Hines C. The Pathophysiology of Intestinal Bacterial Overgrowth Syndromes. Arch Intern Med. 1980;140(10):1349-1352. doi:10.1001/archinte.1980.00330210097030