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Antimicrobial Agents and Chemotherapy, November 2000, p. 3210-3212, Vol. 44, No. 11
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Resistance to Methotrexate Due to AcrAB-Dependent Export from Escherichia coli

Stephan J. Kopytek,dagger John C. D. Dyer, Gwendowlyn S. Knapp, and James C. Hu*

Department of Biochemistry and Biophysics and Center for Advanced Biomolecular Research, Texas A&M University, College Station, Texas 77843-2128

Received 27 March 2000/Returned for modification 1 July 2000/Accepted 12 August 2000

Many laboratory strains of Escherichia coli are resistant to methotrexate (MTX), a folate analogue that binds dihydrofolate reductase (DHFR). Mutations that inactivate either tolC or acrA confer MTX sensitivity. Further, overexpression of a fusion protein with DHFR activity reverses this sensitivity by titrating out intracellular MTX. These results suggest that MTX accumulates in cells where mutations in acrA or tolC have inactivated the TolC-dependent AcrAB multidrug resistance efflux pump.

* Corresponding author. Mailing address: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128. Phone: (979) 862-4054. Fax: (979) 845-4946. E-mail: jimhu{at}tamu.edu.

dagger Present address: Columbia University, Department of Chemistry, New York, NY 10027.

Antimicrobial Agents and Chemotherapy, November 2000, p. 3210-3212, Vol. 44, No. 11
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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