Contribution of integrons, and SmeABC and SmeDEF efflux pumps to multidrug resistance in clinical isolates of Stenotrophomonas maltophilia.

OBJECTIVES The contribution of integrons and efflux pumps to multidrug resistance in Stenotrophomonas maltophilia was evaluated. MATERIALS AND METHODS Ninety-three S. maltophilia clinical isolates were studied. PCR and direct sequencing were used to detect the presence of integrons. Real-time PCR was performed to assess and quantify the expression of the Sme efflux pumps of S. maltophilia. RESULTS Class 1 integrons were detected in 22% of clinical isolates and carried cassettes conferring resistance mainly to aminoglycosides and trimethoprim. The small multidrug resistance gene, smr, was found on class 1 integrons in six isolates. Thirty-one percent of the isolates overexpressed the smeDEF gene, as compared with a control strain, and 59% overexpressed the smeABC gene. Extrusion of ciprofloxacin and meropenem was specific to the SmeABC and SmeDEF pumps, respectively. CONCLUSION SmeABC and SmeDEF efflux pumps play important roles in resistance of S. maltophilia to ciprofloxacin and meropenem.