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Antimicrobial Agents and Chemotherapy, September 2004, p. 3332-3337, Vol. 48, No. 9
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.9.3332-3337.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Plasmid-Encoded Multidrug Efflux Pump Conferring Resistance to Olaquindox in Escherichia coli

Lars Hestbjerg Hansen,* Elsebetta Johannesen, Mette Burmølle, Anders Hay Sørensen,{dagger} and Søren J. Sørensen

Department of Microbiology, University of Copenhagen, Copenhagen, Denmark

Received 3 March 2004/ Returned for modification 14 April 2004/ Accepted 17 May 2004

We report here the first gene-encoded resistance mechanism to the swine growth enhancer olaquindox. The genetic elements involved in resistance to olaquindox were subcloned and sequenced from a conjugative plasmid isolated from Escherichia coli. The subcloned fragment contained two open reading frames, oqxA and oqxB, that are homologous to several resistance-nodulation-cell-division family efflux systems from different species. The putative protein sequences were aligned to both experimentally verified and putative efflux pumps. We show that oqxA and oqxB are expressed in E. coli. Plasmids containing the oqxAB genes yielded high (>128 µg/ml) resistance to olaquindox in E. coli, whereas strains containing the control plasmid showed low resistance to the drug (8 µg/ml). The oqxAB-encoded pump also conferred high (>64 µg/ml) resistance to chloramphenicol. We demonstrate that the subcloned fragment conferred H+-dependent ethidium efflux abilities to E. coli strain N43. In addition, we show that the efflux system is dependent on the host TolC outer membrane protein when expressed in E. coli.

* Corresponding author. Mailing address: Department of Microbiology, University of Copenhagen, Sølvgade 83H, 1307 Copenhagen K, Denmark. Phone: 45-35-32-20-53. Fax: 45-35-32-20-40. E-mail: hestbjerg{at}mermaid.molbio.ku.dk.

{dagger} Present address: Danish Veterinary Institute, DK-1790 Copenhagen V, Denmark.

Antimicrobial Agents and Chemotherapy, September 2004, p. 3332-3337, Vol. 48, No. 9
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.9.3332-3337.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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