The biofilms formed by four out of seven strong slime-producer strains, after a 24-h incubation, are reported in Fig. 7, in which the typical tridimensional shape of a mature biofilm

is clearly evident in all the observed samples. Further, for the weak slime-producer strains of C. difficile, and P. bivia (Fig. 8) as well as for the two isolated strains of C. fallax (data not shown), it was possible to obtain a moderate development of a biofilm community after 48–72 h. A number of papers have reported possible hypotheses on the mechanisms presumably involved in the clogging phenomenon of biliary endoprostheses (for a review, see Donelli et al., 2007). To address the issue of how a biofilm could reach such a thickness to significantly narrow the lumen of the stent, it must be remembered that the biofilm exopolysaccharide matrix engulfs VX809 a number of ‘foreign bodies’ of different sizes including proteins, microbial byproducts, amorphous

calcium bilirubinate and crystals of fatty acid calcium Selleck Rapamycin salts, as well as large-sized dietary fibers (Groen et al., 1987; Leung et al., 1988; Sung et al., 1993; Basoli et al., 1999; Di Rosa et al., 1999; van Berkel et al., 2005). Bile viscosity, which differs on the basis of a patient’s health status, is another parameter to be considered. According to Poiseuille’s law, if the bile viscosity increases, the maintenance of the same bile flow would require an increase in the inner stent diameter: it has been calculated that an increase of 0.2 mm in the inner stent diameter corresponds to a 300% increase in bile flow (Rey et al., 1985). In fact, the narrowing of the stent lumen, as a consequence of biofilm development, causes the slowing of bile flow, promoting both spontaneous and bacteria-driven bile salt precipitation. Thus, considering a mean bacterial

Olopatadine diameter of about 1 μm, a reduction of 0.2 mm in a 10-Fr polyethylene stent (inner diameter 2.4 mm) would correspond to a biofilm of 200 overlapping bacterial layers. However, as already mentioned, the actual thickness of each bacterial layer is expected to be much higher because of the continuous engulfment of large-sized ‘foreign bodies.’ Further, the additional thickness of the host protein conditioning film, layered on the polymeric stent surface and known to mediate microbial attachment via specific adhesins, must be considered. This model, based on the progressive reduction of the stent lumen as a consequence of the multispecies biofilm expected to develop in the peculiar luminal microenvironment of a biliary stent, can be considered, in our opinion, to be a reasonable way to approach the critical issue of stent clogging. Moreover, the accumulation of biliary sludge is thought to be a multifactorial process in which, other than microbial growth, slime production and biofilm formation, the activity of some bacterial enzymes is involved. It is known that β-glucuronidase, produced by E.