This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Elkins, C. A.
Right arrow Articles by Mullis, L. B.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Elkins, C. A.
Right arrow Articles by Mullis, L. B.

 Previous Article  |  Next Article 

Antimicrobial Agents and Chemotherapy, March 2007, p. 923-929, Vol. 51, No. 3
0066-4804/07/$08.00+0     doi:10.1128/AAC.01048-06

Substrate Competition Studies Using Whole-Cell Accumulation Assays with the Major Tripartite Multidrug Efflux Pumps of Escherichia coli{triangledown}

Christopher A. Elkins* and Lisa B. Mullis

Division of Microbiology, National Center for Toxicological Research, United States Food and Drug Administration, Jefferson, Arkansas 72079-9502

Received 21 August 2006/ Returned for modification 25 September 2006/ Accepted 26 December 2006

AcrAB-TolC is the major, constitutively expressed tripartite multidrug efflux system in Escherichia coli that recognizes various structurally unrelated molecules, including many antibiotics, dyes, and steroids. The AcrB inner membrane pump portion of the efflux system has been shown in recent structural studies to bind substrates at multiple sites, suggesting that particular substrate "sets" may compete for efflux by interfering with a certain binding site(s). However, our data indicate that the general structural class does not appear to dictate a particular substrate binding site that can be competitively inhibited in whole cells. In our study, substrate competition failed to increase cell-associated levels of steroids or dyes to levels characteristic of AcrB- or AcrB/EmrAB-deficient genomic mutants or achieved with the pump inhibitor carbonyl cyanide m-chlorophenylhydrazone. In addition, this general observation was sustained even with (i) a cocktail containing seven-pump substrates supplied slightly below their respective wild-type MIC levels, (ii) competing drug substrates of the same structural class (steroids or macrolides), and (iii) hyper-MIC levels of the exogenously supplied agents. Thus, this pump system (and possibly EmrAB-TolC) may have an extraordinary capacity to simultaneously handle multiple-drug substrates that is not necessarily reflected in MIC analyses. In addition, our study has extended the range of substrates recognized by the AcrAB- and EmrAB-TolC systems.

* Corresponding author. Mailing address: Division of Microbiology, National Center for Toxicological Research, 3900 NCTR Drive, Jefferson, AR 72079-9502. Phone: (870) 543-7547. Fax: (870) 543-7307. E-mail: chris.elkins{at}fda.hhs.gov.

{triangledown} Published ahead of print on 8 January 2007.

Antimicrobial Agents and Chemotherapy, March 2007, p. 923-929, Vol. 51, No. 3
0066-4804/07/$08.00+0     doi:10.1128/AAC.01048-06




This article has been cited by other articles:

  • Tikhonova, E. B., Dastidar, V., Rybenkov, V. V., Zgurskaya, H. I. (2009). Kinetic control of TolC recruitment by multidrug efflux complexes. Proc. Natl. Acad. Sci. USA 106: 16416-16421 [Abstract] [Full Text]  


Copyright © 2009 by the American Society for Microbiology.   For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»