The use of various medical devices including indwelling vascular catheters, cardiac pacemakers, prosthetic heart valves, chronic ambulatory peritoneal dialysis catheters and prosthetic joints has greatly facilitated the management of serious medical and surgical illness. However, the successful development of synthetic materials and introduction of these artificial devices into various body systems has been accompanied by the ability of microorganism to adhere to these devices in the environment of biofilms that protect them from the activity of antimicrobial agents and from host defense mechanisms. A number of host, biomaterial and microbial factors are unique to the initiation, persistence and treatment failures of device-related infections. Intravascular catheters are the most common devices used in clinical practice and interactions associated with these devices are the leading cause of nosocomial bacteremias. The infections associated with these devices include insertion site infection, septic thrombophlebitis, septicemia, endocarditis and metastatic abscesses. Other important device-related infections include infections of vascular prostheses, intracardiac prostheses, total artificial hearts, indwelling urinary catheters, orthopedic prostheses, endotracheal tubes and extended wear lenses. The diagnosis and management of biofilm-associated infections remain difficult but critical issues. Appropriate antimicrobial therapy is often not effective in eradicating these infections and the removal of the device becomes necessary. Several improved diagnostic and therapeutic modalities have been reported in recent experimental studies. The clinical usefulness of these strategies remains to be determined.

The interaction between four fluoroquinolones (ciprofloxacin, norfloxacin, pefloxacin, and ofloxacin) and biofilms of Pseudomonas aeruginosa in wells of microtiter plates and on segments of vascular catheters was studied in an in vitro model of vascular catheter colonization. Subinhibitory concentrations (one-half, onefourth, and one-eighth of the MIC) of the fluoroquinolones reduced the adherence of P. aeruginosa to 30 to 33, 44 to 47, and 61 to 67% of that of controls, respectively. The addition of high concentrations of the fluoroquinolones (12.5 and 400 g/ml) to preformed biofilms (grown for 48 h at 37؇C) decreased the adherence of P. aeruginosa to 69 to 77 and 39 to 60% of that of controls, respectively. In an in vitro model of vascular catheter colonization, subinhibitory concentrations (one-half, one-fourth, and one-eighth of the MIC) of fluoroquinolones reduced the number of adherent bacteria to 21 to 23, 40 to 46, and 55 to 70% of that of the controls, respectively. Scanning electron microscopy demonstrated a significant reduction in glycocalyx formation and adherent bacteria in the presence of pefloxacin at one-half to one-eighth of the MIC. Vascular catheter segments precolonized with P. aeruginosa for 24 h and exposed to the fluoroquinolones at 4 to 25 times the MIC (50 g/ml) for 2 h showed <5% growth of adherent cells compared with controls. No adherent organisms were cultured in the presence of 8 to 50 times the MIC (100 g/ml). Scanning electron microscopy studies of preformed biofilms exposed to pefloxacin verified the results obtained by culture. These data show that subinhibitory concentrations of ciprofloxacin, norfloxacin, pefloxacin, and ofloxacin inhibit the adherence of P. aeruginosa to plastic surfaces and vascular catheters. Clinically achievable concentrations of fluoroquinolones (50 to 100 g/ml) were able to eradicate preformed biofilms on vascular catheters.The use of various medical devices such as indwelling vascular catheters, cardiac pacemakers, prosthetic heart valves, chronic ambulatory peritoneal dialysis catheters, and prosthetic joints has greatly facilitated the medical and surgical management of serious illnesses. Bacterial infections following colonization and biofilm formation on these devices are a major cause of morbidity in patients receiving prosthetic devices (5). Biofilms have also been demonstrated on tissues in chronic bacterial diseases that are characterized by resistance to antimicrobial chemotherapy (27). Extracellular slime or glycocalyx production is an important factor in the adherence of bacteria and their protection from host defense mechanisms. Extensive glycocalyx production has been demonstrated on cultures of Staphylococcus epidermidis (14), S. aureus (4), Pseudomonas aeruginosa (15), Escherichia coli (3), and Bacteroides species (16).Different approaches (including the use of various antimicrobial agents) to the eradication of biofilm bacteria have been studied. The combination of tobramycin and piperacillin (1), the combination of tosufloxacin and er...

No abstract

During a prospective study of indwelling vascular catheter-related infections, 134 isolates of Staphylococcus epidermidis were grown from 700 catheter tips. In vitro antimicrobial susceptibility testing of these isolates to oxacillin, vancomycin and ofloxacin was performed using the standard broth microdilution technique. These results were compared to those for the same organisms grown in biofilm before the addition of antimicrobial agents. In 96-well flat bottom microtiter plates, 10(4)-10(5) colony forming units of S. epidermidis in 0.1 ml broth were grown for 18 h at 37 degrees C, at which time a biofilm was observed for all isolates. Different concentrations of antimicrobial agents (0.1 ml) were then added to the plates. The plates were incubated for 18 h at 37 degrees C. Since MICs could not be estimated in these plates, all the wells were subcultured after mixing the biofilm with the broth. Minimum bactericidal concentrations (MBCs) were defined as 99.9% reduction in colony forming units. For organisms grown in suspension, 100% of the isolates were susceptible to vancomycin, 81% to ofloxacin and 40% to oxacillin. MBCs of susceptible isolates were within four-fold differences for vancomycin (53%), oxacillin (50%), and ofloxacin (51%). When grown as a biofilm, 78%, 93% and 71% of isolates had MBCs of> or = 2048 micrograms ml-1 of oxacillin, vancomycin and ofloxacin respectively. These data demonstrate the reduced bactericidal activity of antimicrobial agents against S. epidermidis in a biofilm and a simple method for its detection in the microbiology laboratory.

No abstract