The MarR-Type Repressor MhqR Confers Quinone and Antimicrobial Resistance in <i>Staphylococcus aureus</i>

Abstract

<b><i>Aims:</i></b> Quinone compounds are electron carriers and have antimicrobial and toxic properties due to their mode of actions as electrophiles and oxidants. However, the regulatory mechanism of quinone resistance is less well understood in the pathogen <i>Staphylococcus aureus</i>. <b><i>Results:</i></b> Methylhydroquinone (MHQ) caused a thiol-specific oxidative and electrophile stress response in the <i>S. aureus</i> transcriptome as revealed by the induction of the PerR, QsrR, CstR, CtsR, and HrcA regulons. The <i>SACOL2531-29</i> operon was most strongly upregulated by MHQ and was renamed as <i>mhqRED</i> operon based on its homology to the <i>Bacillus subtilis</i> locus. Here, we characterized the MarR-type regulator MhqR (SACOL2531) as quinone-sensing repressor of the <i>mhqRED</i> operon, which confers quinone and antimicrobial resistance in <i>S. aureus</i>. The <i>mhqRED</i> operon responds specifically to MHQ and less pronounced to pyocyanin and ciprofloxacin, but not to reactive oxygen species (ROS), hypochlorous acid, or aldehydes. The MhqR repressor binds specifically to a 9-9 bp inverted repeat (MhqR operator) upstream of the <i>mhqRED</i> operon and is inactivated by MHQ <i>in vitro</i>, which does not involve a thiol-based mechanism. In phenotypic assays, the <i>mhqR</i> deletion mutant was resistant to MHQ and quinone-like antimicrobial compounds, including pyocyanin, ciprofloxacin, norfloxacin, and rifampicin. In addition, the <i>mhqR</i> mutant was sensitive to sublethal ROS and 24 h post-macrophage infections but acquired an improved survival under lethal ROS stress and after long-term infections. <b><i>Innovation:</i></b> Our results provide a link between quinone and antimicrobial resistance <i>via</i> the MhqR regulon of <i>S. aureus</i>. <b><i>Conclusion:</i></b> The MhqR regulon was identified as a novel resistance mechanism towards quinone-like antimicrobials and contributes to virulence of <i>S. aureus</i> under long-term infections.