Bacterial Flora of the Human Small Intestine

The literature regarding the normal bacterial flora of the human gastrointestinal tract has recently been reviewed by Rosebury¹ and Donaldson,² and can be summarized as follows: the stomach or upper small intestine may be sterile or contain a sparse bacterial population; those bacteria found in the upper portion of the gastrointestinal tract are considered to be contaminants from the mouth and respiratory tract, and seldom exceed counts of 10⁵ bacteria per milliliter of intestinal content; although bacteria in the terminal ileum are often of the fecal type, about 50% of specimens are sterile; an entirely different situation prevails in the colon which is more stagnant and supports a large and varied bacterial population.

Intestinal Bacteria  Our interest in human small intestinal flora arose from research into the lethal role of intestinal bacteria and their products during intestinal strangulation obstruction.^3,4 These studies have been concerned with normal