Date Published: October 13, 2016
Publisher: Public Library of Science
Author(s): Zhe-Xian Tian, Xue-Xian Yi, Anna Cho, Fergal O’Gara, Yi-Ping Wang, Matthew R. Parsek.
Resistance-Nodulation-Division (RND) efflux pumps are responsible for multidrug resistance in Pseudomonas aeruginosa. In this study, we demonstrate that CpxR, previously identified as a regulator of the cell envelope stress response in Escherichia coli, is directly involved in activation of expression of RND efflux pump MexAB-OprM in P. aeruginosa. A conserved CpxR binding site was identified upstream of the mexA promoter in all genome-sequenced P. aeruginosa strains. CpxR is required to enhance mexAB-oprM expression and drug resistance, in the absence of repressor MexR, in P. aeruginosa strains PA14. As defective mexR is a genetic trait associated with the clinical emergence of nalB-type multidrug resistance in P. aeruginosa during antibiotic treatment, we investigated the involvement of CpxR in regulating multidrug resistance among resistant isolates generated in the laboratory via antibiotic treatment and collected in clinical settings. CpxR is required to activate expression of mexAB-oprM and enhances drug resistance, in the absence or presence of MexR, in ofloxacin-cefsulodin-resistant isolates generated in the laboratory. Furthermore, CpxR was also important in the mexR-defective clinical isolates. The newly identified regulatory linkage between CpxR and the MexAB-OprM efflux pump highlights the presence of a complex regulatory network modulating multidrug resistance in P. aeruginosa.
Pseudomonas aeruginosa, a major pathogen associated with cystic fibrosis, is known for its intrinsic resistance to a wide range of antimicrobial agents and its ability to develop multidrug resistance following antibiotic therapy . Resistance-Nodulation-Division (RND) efflux systems are largely responsible for intrinsic and acquired multidrug resistance in P. aeruginosa; genes encoding 12 RND efflux pumps have been identified in its genome [2, 3].
In this work, we applied comparative genomic analysis to illuminate the regulatory networks responsible for modulating RND efflux pump expression in P. aeruginosa. Similar comparative genomic analysis has been performed to identify novel regulons based on conserved DNA motifs on the promoter regions of potential target genes as binding sites of global regulators [7, 48, 49]. With the accumulation of whole-genome sequencing and transcriptomic data, comparative genomic analysis has become a powerful approach for identifying common or species-specific genetic regulatory networks among different species.