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Antimicrobial Agents and Chemotherapy, May 1999, p. 1085-1090, Vol. 43, No. 5
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Negative Regulation of the Pseudomonas aeruginosa Outer Membrane Porin OprD Selective for Imipenem and Basic Amino Acids

Martina M. Ochs, Matthew P. McCusker, Manjeet Bains, and Robert E. W. Hancock*

Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3

Received 10 November 1998/Returned for modification 29 January 1999/Accepted 7 March 1999

Pseudomonas aeruginosa OprD is a specific porin which facilitates the uptake of basic amino acids and imipenem, a carbapenem antibiotic. Resistance to imipenem due to the loss of OprD is an important mechanism for the loss of clinical effectiveness. To investigate the negative regulatory mechanisms influencing oprD expression, a gene upstream of the coregulated mexEF-oprN efflux operon, designated mexT, was cloned. The predicted 304-amino-acid mature MexT protein showed strong homology to LysR-type regulators. When overexpressed it induced the expression of the mexEF-oprN efflux operon while decreasing the level of expression of OprD. The use of an oprD::xylE transcriptional fusion indicated that it acted by repressing the transcription of oprD. Salicylate, a weak aromatic acid known to reduce porin expression and induce low levels of multiple antibiotic resistance in Escherichia coli, was able to induce imipenem resistance and reduce the expression of OprD but not multiple antibiotic resistance or OprN expression in P. aeruginosa. This was also demonstrated to occur at the level of transcription. Acetyl salicylate and benzoate, but not catechol, were also able to reduce the levels of OprD in the P. aeruginosa outer membranes. These OprD-suppressing compounds increased imipenem resistance even in a mexT-overexpressing and nfxC mutant backgrounds, suggesting that such resistance is independent of the MexT repressor and that oprD is influenced by more than a single mechanism of repression.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada. Phone: (604) 822-2682. Fax: (604) 822-6041. E-mail: bob{at}cmdr.ubc.ca.

Antimicrobial Agents and Chemotherapy, May 1999, p. 1085-1090, Vol. 43, No. 5
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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