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JAC Advance Access originally published online on July 29, 2009
Journal of Antimicrobial Chemotherapy 2009 64(4):731-734; doi:10.1093/jac/dkp271
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© The Author 2009. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Original research

Molecular cloning and characterization of SmrA, a novel ABC multidrug efflux pump from Stenotrophomonas maltophilia

Arif Al-Hamad1,*, Mathew Upton1 and James Burnie1,2

1 Medical Microbiology, School of Medicine, University of Manchester, 2nd Floor Clinical Sciences Building, Manchester Royal Infirmary, Manchester M13 9WL, UK 2 Clinical Microbiology, Central Manchester University Hospitals NHS Foundation Trust, 2nd Floor Clinical Sciences Building, Manchester Royal Infirmary, Manchester M13 9WL, UK

Received 10 May 2009; returned 22 May 2009; revised 27 May 2009; accepted 2 July 2009

* Corresponding author. Tel: +44 161 276 8823; Fax: +44 161 276 8826; E-mail: arifhamad{at}doctors.org.uk

Objectives: Stenotrophomonas maltophilia is an emerging nosocomial pathogen that can cause difficult-to-treat infections and exhibits significant degrees of poorly understood multidrug resistance (MDR). The aim of this study was to identify and characterize a multidrug ATP-binding cassette (ABC) efflux pump in S. maltophilia.

Methods: SmrA was identified in the S. maltophilia genome based on the detection of ABC transporter conserved motifs and alignment with experimentally proven MDR ABC transporters. The smrA gene was cloned and expressed in the hypersusceptible acrAB mutant Escherichia coli strain SM1411. The resistance to several antimicrobial agents was tested using Stokes' disc diffusion and broth microdilution MIC methods. Norfloxacin accumulation and efflux assays were performed using a fluorescence method with and without the efflux pump inhibitors sodium O-vanadate and reserpine.

Results: Cloning and expression of smrA in Escherichia coli conferred increased resistance to structurally unrelated compounds, including fluoroquinolones, tetracycline, doxorubicin and multiple dyes. Moreover, the expression of smrA in E. coli reduced norfloxacin uptake and enhanced its efflux, features that could be inhibited by the ABC efflux pump inhibitors.

Conclusions: SmrA is a member of the ABC multidrug efflux pump family. The findings warrant further study of the role of this molecule in S. maltophilia isolates, to estimate the potential impact of this system in antimicrobial resistance.

Keywords: ABC transporters , multidrug exporter , antibiotic resistance , multidrug resistant


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