ABSTRACT
Any de—nition of small intestinal bacterial overgrowth (SIBO) must differentiate between SIBO itself and the SIBO syndrome. Essential to the de—nition of SIBO is the concept that under conditions of health, the small intestine, via a number of mechanisms, keeps the number of bacteria populating it very low. An increased number of bacteria within the small intestinal lumen is the sine qua non of SIBO. By convention, >105 colony forming units per milliliter of small intestinal «uid (CFU/ mL) are the accepted minimum number of bacteria that de—ne bacterial overgrowth [1]. However, as described in detail later in this chapter, pitfalls exist in accepting this number too strictly.
