IS THERE A SYNERGISTIC EFFECT BETWEEN MIXED BACTERIAL-INFECTION IN BIOFILM FORMATION ON BILIARY STENTS

Background: Biliary sludge which forms as a result of bacterial adhere nce and biofilm formation in the biliary system is a recognized cause of blockage of plastic stents. Bacteriological cultures of sludge have revealed a mixed infection with gram-positive and gram-negative bacte ria. Animal studies have shown that prophylactic ciprofloxacin, which selectively suppress gram-negative bacteria, results in prolonged sten t patency despite colonization of the stents by gram-positive bacteria . Methods: We tested a possible synergistic effect between gram-negati ve and gram-positive bacteria in adherence and biofilm formation on pl astic stents. Clinical isolates of Escherichia coli and Enterococcus w ere cultured in separate chemostats to achieve a steady growth. Adhere nce of the two bacteria on plastic stent surface were tested separatel y by perfusing infected bile with the respective bacteria through diff erent modified Robbins devices containing 10F polyethylene stent piece s up to 4 days. In a second experiment, Enterococcus was perfused thro ugh stent pieces precolonized with E. coli for 24 hours. The stent pie ces were then removed daily and analyzed by bacteriologic culture and scanning electron microscopy for bacterial adherence and biofilm forma tion. Results: Gram-negative E. coli were more adherent than gram-posi tive Enterococcus. Precolonization with E. coli facilitates subsequent attachment of Enterococcus. Conclusions: We concluded that there is a synergistic effect between grampositive and gram-negative bacteria in adherence and biofilm formation.