Alterations of intestinal microflora by antibiotics. Effects on fecal excretion, transit time, and colonic motility in rats.

The effects of intragastric antibiotics in rats were examined on fecal microflora and excretion and through transit time and cecocolonic myoelectric activity. A solution of nonabsorbable antibiotics infused into the stomach for 20 days had a dramatic effect on the quantity, composition, and bacterial content of rat feces. Both the dry weight and the water content of feces were increased. The amount of short-chain fatty acids in the feces was dramatically lowered. However, neither total nor cecocolonic transit time of solids was affected. The cyclic organization of cecocolonic myoelectric activity was altered by antibiotic treatment, and the motility index, ie, the quantity of myoelectric activity recorded on the colon, progressively increased. An infusion of short-chain fatty acids modified this motor pattern but did not restore activity to a level comparable to that of control animals. In conclusion, intragastric antibiotics dramatically reduced intestinal microflora and increased fecal excretion of dry matter and water but did not affect the transit time of solid gut contents, although they did influence cecocolonic motility.