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.