Antibacterial activity of bile salts against common biliary pathogens. Effects of hydrophobicity of the molecule and in the presence of phospholipids.

In vitro studies have demonstrated that bile salts have cytotoxic and bacteriostatic properties. The cytotoxic effect of bile salts is reduced when lecithin is added. The effect of lecithin on the bacteriostatic property of bile salts is not known. In this report, we test the hypotheses that (1) the bacteriostatic activity of bile salts is a function of the hydrophobicity of the molecules, and (2) lecithin, by engaging the hydrophobic component of bile salts, attenuates the bacteriostatic property of these molecules. Two common biliary pathogens, Escherichia coli and Enterococcus fecalis, were tested in this experiment. The results demonstrate that hydrophobic bile salts (sodium taurodeoxycholate, sodium deoxycholate) have more significant inhibition on the growth of bacteria when compared with the hydrophilic bile salts (sodium taurocholate, sodium chenodeoxycholate, and sodium tauroursodeoxycholate). When lecithin is added, creating a mixed micellar solution and mimicking the in vivo conditions, the antibacterial activities of even the more potent bacteriostatic bile salts are significantly reduced. The finding that lecithin significantly attenuates the bacteriostatic property of even the hydrophobic bile salts raises questions about the clinical significance of such bacteriostatic effect in vivo; as bile salts in the bile exist in mixed micellar solution.