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Antimicrobial Agents and Chemotherapy, July 1999, p. 1719-1724, Vol. 43, No. 7
Center for Adaptation Genetics and Drug
Resistance1 and Departments of Molecular
Biology and Microbiology2 and
of Medicine,3 Tufts University
School of Medicine, Boston, Massachusetts 02111
Received 10 December 1998/Returned for modification 1 February
1999/Accepted 21 April 1999
Active efflux is a useful strategy by which bacteria evade growth
inhibition by antibiotics. Certain semisynthetic tetracycline (TC)
analogs, substituted at the 13th carbon at C-6 on ring C of the TC
molecule, blocked TC efflux as revealed in everted membrane vesicles
from class B TC-resistant (Tcr) Escherichia
coli (M. L. Nelson, B. H. Park, J. S. Andrews,
V. A. Georgian, R. C. Thomas, and S. B. Levy, J. Med. Chem. 36:370-377, 1993). A representative C-13-substituted
analog, 13-cyclopentylthio-5-OH-TC (13-CPTC), was shown to
competitively inhibit TC translocation by the Tet(B) protein, blocking
the uptake of TC into vesicles and therefore the efflux of TC from
whole cells. Against Tcr E. coli, 13-CPTC, when
used in combination with doxycycline, produced synergistic inhibition
of growth. 13-CPTC was shown to increase the uptake of
[3H]TC into the resistant cells. 13-CPTC alone was a
potent growth inhibitor against TC-susceptible (Tcs) and
Tcr Staphylococcus aureus and enterococci
specifying class K or class L efflux-dependent TC resistance mechanisms
or, unexpectedly, the class M ribosomal protection mechanism. These
findings indicate that derivatives of TC, identified by their ability
to block the Tet(B) efflux protein, can restore TC activity against
Tcr bacteria bearing either of the two known resistance
mechanisms. Blocking drug efflux and increasing intracellular drug
concentrations constitute an effective approach to reversing TC
resistance and may be generally applicable to other antibiotics
rendered ineffective by efflux proteins.
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Reversal of Tetracycline Resistance Mediated by
Different Bacterial Tetracycline Resistance Determinants by an
Inhibitor of the Tet(B) Antiport Protein
*
Corresponding author. Mailing address: Center for
Adaptation Genetics and Drug Resistance, Tufts University School of
Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636-6764. Fax: (617) 636-0458. E-mail: slevy{at}opal.tufts.edu.
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