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Antimicrobial Agents and Chemotherapy, August 1998, p. 1938-1943, Vol. 42, No. 8
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Characterization of the MexC-MexD-OprJ Multidrug Efflux System in Delta mexA-mexB-oprM Mutants of Pseudomonas aeruginosa

Naomasa Gotoh,1,* Hideto Tsujimoto,1 Masataka Tsuda,2 Kiyomi Okamoto,1 Atsuko Nomura,1 Takaomi Wada,1 Masaaki Nakahashi,1 and Takeshi Nishino1

Department of Microbiology, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414,1 and Department of Biology, Faculty of Science, Okayama University, Okayama 700-8530,2 Japan

Received 4 August 1997/Returned for modification 26 November 1997/Accepted 22 May 1998

Expression of the multidrug efflux system MexC-MexD-OprJ in nfxB mutants of Pseudomonas aeruginosa contributes to resistance to fluoroquinolones and the "fourth-generation" cephems (cefpirome and cefozopran), but not to most beta -lactams, including the ordinary cephems (ceftazidime and cefoperazone). nfxB mutants also express a second multidrug efflux system, MexA-MexB-OprM, due to incomplete transcriptional repression of this operon by the mexR gene product. To characterize the contribution of the MexC-MexD-OprJ system to drug resistance in P. aeruginosa, a site-specific deletion method was employed to remove the mexA-mexB-oprM region from the chromosome of wild-type and nfxB strains of P. aeruginosa. Characterization of mutants lacking the mexA-mexB-oprM region clearly indicated that the MexC-MexD-OprJ efflux system is involved in resistance to the ordinary cephems as well as fluoroquinolones and the fourth-generation cephems but not to carbenicillin and aztreonam. Rabbit polyclonal antisera and murine monoclonal antibody against the components of the MexA-MexB-OprM system were prepared and used to demonstrate the reduced production of this efflux system in the nfxB mutants. Consistent with this, transcription of the mexA-mexB-oprM operon decreased in an nfxB mutant. This reduction appears to explain the hypersusceptibility of the nfxB mutant to beta -lactams, including ordinary cephems.

* Corresponding author. Mailing address: Department of Microbiology, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan. Phone: 81-75-595-4642. Fax: 81-75-583-2230. E-mail: ngotoh{at}mb.kyoto-phu.ac.jp.

Antimicrobial Agents and Chemotherapy, August 1998, p. 1938-1943, Vol. 42, No. 8
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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