Biofilm Formation by Stenotrophomonas maltophilia : Modulation by Quinolones, Trimethoprim-Sulfamethoxazole, and Ceftazidime

Abstract

We investigated the in vitro effects of seven fluoroquinolones (ciprofloxacin, grepafloxacin, levofloxacin, moxifloxacin, norfloxacin, ofloxacin, and rufloxacin), compared to those of trimethoprim-sulfamethoxazole (SXT) and ceftazidime on total biomass and cell viability of Stenotrophomonas maltophilia biofilm. S. maltophilia attached rapidly to polystyrene, within 2 h of incubation, and then biofilm formation increased over time, reaching maximum growth at 24 h. In the presence of fluoroquinolones at one-half and one-fourth the MIC, biofilm biomass was significantly (P < 0.01) reduced to 55 to 70% and 66 to 76% of original mass, respectively. Ceftazidime and SXT did not exert any activity. Biofilm bacterial viability was significantly reduced by all antibiotics tested at one-half the MIC. At one-fourth the MIC all antibiotics, except levofloxacin, significantly reduced viability. Treatment of preformed biofilms with bactericidal concentrations (500, 100, and 50 g/ml) of all fluoroquinolones caused, except for norfloxacin, significant reduction of biofilm biomass to 29.5 to 78.8, 64.1 to 83.6, and 70.5 to 82.8% of original mass, respectively. SXT exerted significant activity at 500 g/ml only. Ceftazidime was completely inactive. Rufloxacin exhibited the highest activity on preformed biofilm viability, significantly decreasing viable counts by 0.6, 5.4, and 17.1% at 500, 100, and 50 g/ml, respectively. Our results show that (i) subinhibitory (one-half and one-fourth the MIC) concentrations of fluoroquinolones inhibit adherence of S. maltophilia to polystyrene and (ii) clinically achievable concentrations (50 and 100 g/ml) of rufloxacin are able to eradicate preformed S. maltophilia biofilm.The use of synthetic materials for temporary or permanent implantation-i.e., central venous catheters, urinary catheters, intraocular lenses, and prosthetic heart valves-has been accompanied by the emergence of implant-associated infection. The bacterial infections following colonization and biofilm formation on these prosthetic materials represent the principal cause of morbidity in patients undergoing prosthetic implantation (6). The production of extracellular slime or glycocalyx is a crucial factor in the adherence of bacteria and their protection from host defense mechanisms and effects of antimicrobial agents. It has become clear that biofilm-grown cells express properties distinct from those of planktonic cells, one of which is an increased resistance to antimicrobial agents. Standard antimicrobial treatments typically fail to eradicate biofilms, which can result in chronic infection and the need for surgical removal of afflicted areas.Stenotrophomonas maltophilia is being reported with increasing frequency as an important nosocomial pathogen. It is an opportunistic pathogen colonizing patients in intensive care settings, especially those with underlying debilitating conditions such as immunosuppression, malignancies, and implantation of foreign devices (catheters, respiratory therapy equipment, etc.). Bacterial adherenc...

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