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Endoscopic biliary stents provide effective palliation of malignant obstructive jaundice in patients who are not surgical candidates. Unfortunately the stents in current use have a tendency to block. The clogging phenomenon also severely restricts the value of stents in patients with benign strictures. We studied the mechanism of the occlusion of biliary stents to find ways to prevent it. We have examined 17 blocked stents by electron microscopy(EM), infrared absorption spectrophotometry, and bacteriological cultures. The mean time to stent clogging with 10 french stents was 131 days, and with 12 French stents was 143 days. The differece between the clogging time of the two stents was statistically not sigificant. Scanning EM showed that the internal surfaces of the stent were covered with bacteria embedded in a condensed fibrillar intercellular matrix. The bacteris form a surrounding fibrillar extracellular product which anchors them to the stent. Inorganic crystals were rarely seen, because they presumable dissolved during the fixing for EM. These EM findings are typical of a biofilm. As major components of the occluding material calcium bilirubinate was identified in 15 stents by infrared absorption spectrophotometry. 7 different microorgainsms were isolated from the 17 blocked biliary stents. 6 of the isolates were gram-negative, and 1 was gram-positive. The most frequently isolated genus was Escherichia, which was found in 8 stents, followed by proteus, Pseudomonas, and Morganella, which was found in 2 stents respectvely. We propose that stent colgging is initiated by bacterial adhesion and growth of a biofilm. The bacteria then deconjugate bilirubin in bile and the lumen is progressively occluded by deposition of calcium bilirubinate and further biofilm formation.
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