Hydrophobic bile salt inhibits bacterial adhesion on biliary stent material

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Abstract
Blockage of indwelling biliary stents is caused by biliary sludge, which forms as a result of bacteria adhering to the surface of the stent material and forming adherent biofilm. As the adherence of bacteria on plastic surface involves hydrophobic interaction of the plastic polymer and the bacterial cell wall, we tested if the detergent property of bile salts might retard bacterial adherence. Three common biliary pathogens isolated from the bile of patients suffering from acute suppurative cholangitis were used in this experiment:E. coli (O21:H25) which form pili and a glycocalyx;E. coli (O101:H9), non-piliated but with a glycocalyx, andEnterococcus fecalis without either pili or a glycocalyx. Polyethylene disks (1 cm2 diameter) were used for thein vitro adhesion study. They were continuously perfused by the bacterial suspension, flowing at 50 ml/hr at 37°C for 24 hr. The suspending media used were sterile human bile and tryptic soy broth. Two different bile salts, taurocholate and taurodeoxycholate, were added to the perfusion media. The number of bacteria adhering to the surface was assessed by viable bacterial count, epifluorescence microscopy, and scanning electron microscopy. The results showed thatE. coli (O21:H25) exhibited better adherence than the nonpiliatedE. coli (O101:H9), which in turn was better than the non-pili-, non-glycocalyx-producingEnterococcus fecalis. When a more hydrophobic bile salt, taurodeoxycholate, was added at 25 or 50 mM to the tryptic soy broth or to the human bile, the adherence of the twoE. coli strains were reduced 100-to 1000-fold (PEnterococcus fecalis was not influenced by either bile salts. Thus a hydrophobic bile salt can interfere with the binding of the bacterial cell wall (equipped with pili and/or a glycocalyx) to a polyethylene surface, reducing the adherence of bacteria. Altering the bile salt composition of bile offers a potential treatment in postponing stent blockage.