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Journal of Bacteriology, January 2008, p. 648-654, Vol. 190, No. 2
0021-9193/08/$08.00+0 doi:10.1128/JB.01513-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Teruo Kuroda,1* and
Tomofusa Tsuchiya2
Department of Genome Applied Microbiology,1 Department of Molecular Microbiology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Tsushima, Okayama, 700-8530, Japan2
Received 19 September 2007/ Accepted 5 November 2007
We cloned genes, designated smdAB, that encode a multidrug efflux pump from the chromosomal DNA of clinically isolated Serratia marcescens NUSM8906. For cells of the drug-hypersensitive strain Escherichia coli KAM32 harboring a recombinant plasmid carrying smdAB, structurally unrelated antimicrobial agents such as norfloxacin, tetracycline, 4',6-diamidino-2-phenylindole (DAPI), and Hoechst 33342 showed elevated MICs. The deduced amino acid sequences of both SmdA and SmdB exhibited similarities to the sequences of ATP-binding cassette (ABC)-type multidrug efflux pumps. The efflux of DAPI and Hoechst 33342 from E. coli cells expressing SmdAB was observed, and the efflux activities were inhibited by sodium o-vanadate, which is a well-known ATPase inhibitor. The introduction of smdA or smdB alone into E. coli KAM32 did not elevate the MIC of DAPI; thus, both SmdA and SmdB were required for function. These results indicate that SmdAB is probably a heterodimeric multidrug efflux pump of the ABC family in S. marcescens.
Published ahead of print on 16 November 2007.
Present address: Graduate School of Medical and Pharmaceutical Sciences, Kumamoto University, Kumamoto, 862-0973, Japan.
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