In vivo effect of bile salts and cholestyramine on intestinal anaerobic bacteria.

In vitro studies have shown that some bile salts inhibit the growth of intestinal bacteria. We investigated the possibility that bile salts might have a similar action in vivo in the ileum by performing serial anaerobic cultures and bile salt analyses on postprandial ileal fluid obtained anaerobically via intestinal tube. Five subjects were studied under control conditions, and after a 1-week course of orally administered cojugated bile salts in a dose shown to increase the bile salt pool. Three of the subjects were also studied after a 1-week course of cholestyramine. The numebr of ileal anaerobic microorganisms decreased significantly after both bile salt and cholestyramine treatment. Ileal bile salt concentrations were generally high (mean 9.2 mM) and did not change significantly after either bile salt or cholestyramine treatment. The results of this study are unexplained. Although it is possible that bile salts play a role in the regulation of small intestinal anaerobic flora, the lack of a relationship between ileal bile salt concentration and population levels of anaerobic organisms is puzzling and raises further questions about such a role for bile salts.