Two regulators, PA3898 and PA2100, modulate the Pseudomonas aeruginosa multidrug resistance MexAB-OprM and EmrAB efflux-pumps and biofilm formation [Mechanisms of Resistance]

It is generally believed that the Pseudomonas aeruginosa biofilm matrix itself acts as a molecular sieve or sink that contributes to significant levels of drug resistance, but it is becoming more apparent that multidrug efflux-pumps induced during biofilm growth significantly enhances resistance levels. We present here a novel transcriptional regulator, PA3898, which controls biofilm formation and multidrug efflux-pumps in P. aeruginosa. A mutant of this regulator significantly reduced the ability of P. aeruginosa to produce biofilm in vitro, and affected its in vivo fitness and pathogenesis in Drosophila melanogaster and BALB/c mouse lung infection models. Transcriptome analysis revealed that PA3898 modulates essential virulence genes/pathways, including multidrug efflux-pumps and phenazine biosynthesis. ChIP-seq identified its DNA binding sequences and confirmed PA3898 directly interacts with promoter regions of four genes/operons, two of which are mexAB-oprM and phz2. Co-immunoprecipitation revealed a regulatory partner of PA3898 as PA2100, and both are required for binding to DNA in electrophoresis mobility shift assays. PA3898 and PA2100 were given the names MdrR1 and MdrR2, respectively, as novel repressors of the mexAB-oprM multidrug efflux operon and activators for another multidrug efflux pump EmrAB. Interaction between MdrR1 and MdrR2 to the promoter regions of their regulons was further characterized via localized surface plasmon resonance and DNA footprinting. These regulators directly repress the mexAB-oprM operon, independent of its well-established MexR regulator. Mutants of mdrR1 and mdrR2 caused increased resistance to multiple antibiotics in P. aeruginosa, validating the significance of these newly discovered regulators.

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