John F. Inciardi

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 adherence 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 bacteria. Animal studies have shown that prophylactic ciprofloxacin, which selectively suppress gram-negative bacteria, results in prolonged stent patency despite colonization of the stents by gram-positive bacteria. METHODS We tested a possible synergistic effect between gram-negative and gram-positive bacteria in adherence and biofilm formation on plastic stents. Clinical isolates of Escherichia coli and Enterococcus were cultured in separate chemostats to achieve a steady growth. Adherence of the two bacteria on plastic stent surface were tested separately by perfusing infected bile with the respective bacteria through different modified Robbins devices containing 10F polyethylene stent pieces up to 4 days. In a second experiment, Enterococcus was perfused through stent pieces precolonized with E. coli for 24 hours. The stent pieces were then removed daily and analyzed by bacteriologic culture and scanning electron microscopy for bacterial adherence and biofilm formation. RESULTS Gram-negative E. coli were more adherent than gram-positive Enterococcus. Precolonization with E. coli facilitates subsequent attachment of Enterococcus. CONCLUSIONS We concluded that there is a synergistic effect between gram-positive and gram-negative bacteria in adherence and biofilm formation.

In vitro evaluation of antibiotic prophylaxis in the prevention of biliary stent blockage.

BACKGROUND Bacterial adherence and biofilm formation are important factors in the blockage of biliary stents. Clinical studies with oral antibiotic prophylaxis to prevent stent blockage have produced conflicting results. The aim of this study was to evaluate the in vitro effect of single antibiotic (ciprofloxacin, ceftazidime, or ampicillin) treatment on adherence of Escherichia coli and Enterococcus to plastic stents. METHODS Selected clinical isolates of E coli and Enterococcus were perfused through a modified Robbins device containing segments of polyethylene stents. The stents were removed daily and the number of bacteria attached was measured. The effect of antibiotic treatment on bacterial adherence was tested by the perfusion of individual antibiotics into separate modified Robbins devices using a side-arm adaptor and the results were compared with saline controls. RESULTS Compared with the saline controls, ciprofloxacin and ceftazidime caused a 10- to 100-fold reduction in the number of E coli attached to the stents, whereas ampicillin had no effect on adherence of E coli. Ampicillin caused a 5- to 10-fold reduction in Enterococcus adherence but there was no change with ceftazidime. Sustained reduction in E coli adherence was observed with prolonged ciprofloxacin perfusion. CONCLUSION Timely treatment with appropriate antibiotics reduced bacterial adherence in vitro and may be potentially beneficial in the prevention of stent blockage.