Abstract
The antibiotic trimethoprim is frequently used to manage Burkholderia infections, and members of the resistance-nodulation-division (RND) family of efflux pumps have been implicated in multidrug resistance of this species complex. We show here that a member of the distinct Escherichia coli multidrug resistance B (EmrB) family is a primary exporter of trimethoprim in Burkholderia thailandensis, as evidenced by increased trimethoprim sensitivity after inactivation of emrB, the gene that encodes EmrB. We also found that the emrB gene is up-regulated following the addition of gentamicin and that this up-regulation is due to repression of the gene encoding OstR, a member of the multiple antibiotic resistance regulator (MarR) family. The addition of the oxidants H2O2 and CuCl2 to B. thailandensis cultures resulted in OstR-dependent differential emrB expression, as determined by qRT-PCR analysis. Specifically, OstR functions as a rheostat that optimizes emrB expression under oxidizing conditions, and it senses oxidants by a unique mechanism involving two vicinal cysteines and one distant cysteine (Cys3, Cys4, and Cys169) per monomer. Paradoxically, emrB inactivation increased resistance of B. thailandensis to tetracycline, a phenomenon that correlated with up-regulation of an RND efflux pump. These observations highlight the intricate mechanisms by which expression of genes that encode efflux pumps is optimized depending on cellular concentrations of antibiotics and oxidants.
Highlights
The antibiotic trimethoprim is frequently used to manage Burkholderia infections, and members of the resistance-nodulationdivision (RND) family of efflux pumps have been implicated in multidrug resistance of this species complex
Members of the protein family named for E. coli multiple antibiotic resistance regulator (MarR) are ubiquitous in bacterial species, and the most common mode of transcriptional regulation involves binding to the intergenic DNA between the gene encoding the MarR homolog and divergently or adjacently oriented genes, thereby hindering access of RNA polymerase to the promoter
Expression of the B. cepacia Escherichia coli multidrug resistance B (EmrB) ortholog (BcrA) in E. coli resulted in increased resistance to nalidixic acid and tetracycline [22]
Summary
X Ashish Gupta, and X Anne Grove From the Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803
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