The endoscopic insertion of plastic stents represents an effective system of biliary decompression contributing to the regression of symptomatology and determining a significant improvement of quality of life in patients suffering from obstructive jaundice associated with malignant hepatobiliary tumors or benign strictures (Ballinger et al., 1994). However, the major limitations of this palliative approach are mainly represented by stent occlusion, often followed by life-threatening cholangitis necessitating repeated interventions and stent exchange.

Stent occlusion is caused by the deposition of biliary sludge, which is composed of cholesterol crystals, calcium bilirubinate and palmitate, amounts of cholesterol as well as bacteria and/or fungi, microbial byproducts, proteins, dietary fibers and glycoproteins check details (Dowidar et al., 1991; McAllister et al., 1993; Weickert et al., 2001; Moss et al., 2006; Donelli et al., 2007). Deposition of calcium salts due to the biochemical activities of bacterial enzymes in the biofilm growing on the surface of the stents and reflux of intestinal contents into stents have been proposed FK506 clinical trial as the two main mechanisms of stent occlusion (Speer et al., 1988; Moesch et

al., 1991; Sung et al., 1993). However, some authors suggested that microbial adhesion and biofilm formation on the surface of the stent lumen could play an important role in the initiation of the clogging process and in the subsequent stent blockage (Leung et al., 1988, 2000; Basoli et al., 1999; Di Rosa et al., oxyclozanide 1999; van Berkel et al., 2000, 2005; Guaglianone et al., 2008). Microorganisms gain access into the biliary system either by descending via the portal venous circulation or by ascending through the

sphincter of Oddi in duodenal–biliary reflux (Sung et al., 1992). Bacteria adhere to the stent surface and their sessile growth and exopolysaccharide production lead to the establishment of a thick biofilm conferring microorganisms with an efficient protection from both antibacterial agents and phagocytic cells. The β-glucuronidase and lecithinase (or phospholipase C) enzymatic activities of colonizing microorganisms lead to the precipitation of calcium bilirubinate and palmitate, thus contributing to the sludge accumulation within the biliary system and then to the stent occlusion (Leung et al., 1988). The aims of this study were to analyze the biliary sludge of 28 clogged stents to check the presence of ex vivo biofilm formation, to identify all the microbial species colonizing the stents’ lumen and to verify the in vitro ability of isolated anaerobic bacteria to form a biofilm. Twenty-eight clogged biliary stents were removed from patients (mean age=66 years) who had undergone endoscopic stent insertion for the treatment of a variety of diseases involving biliary obstruction. The implantation time ranged from 20 to 484 days (mean=164).