Affiliation:
1. Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202
Abstract
ABSTRACT
The
Mycobacterium smegmatis
genome contains many genes encoding putative drug efflux pumps. Yet with the exception of
lfrA
, it is not clear whether these genes contribute to the intrinsic drug resistance of this organism. We showed first by reverse transcription (RT)-PCR that several of these genes, including
lfrA
as well as the homologues of
Mycobacterium tuberculosis
Rv1145, Rv1146, Rv1877, Rv2846c (
efpA
), and Rv3065 (
mmr
and
emrE
), were expressed at detectable levels in the strain mc
2
155. Null mutants each carrying an in-frame deletion of these genes were then constructed in
M. smegmatis
. The deletions of the
lfrA
gene or
mmr
homologue rendered the mutant more susceptible to multiple drugs such as fluoroquinolones, ethidium bromide, and acriflavine (two- to eightfold decrease in MICs). The deletion of the
efpA
homologue also produced increased susceptibility to these agents but unexpectedly also resulted in decreased susceptibility to rifamycins, isoniazid, and chloramphenicol (two- to fourfold increase in MICs). Deletion of the Rv1877 homologue produced some increased susceptibility to ethidium bromide, acriflavine, and erythromycin. The upstream region of
lfrA
contained a gene encoding a putative TetR family transcriptional repressor, dubbed LfrR. The deletion of
lfrR
elevated the expression of
lfrA
and produced higher resistance to multiple drugs. Multidrug-resistant single-step mutants, independent of LfrA and attributed to a yet-unidentified drug efflux pump (here called LfrX), were selected in vitro and showed decreased accumulation of norfloxacin, ethidium bromide, and acriflavine in intact cells. Finally, use of isogenic β-lactamase-deficient strains showed the contribution of LfrA and LfrX to resistance to certain β-lactams in
M. smegmatis
.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
206 articles.
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