title: Multiple mutations lead to MexXY-OprM-dependent aminoglycoside resistance in clinical strains of Pseudomonas aeruginosa.
abstract: Constitutive overproduction of the pump MexXY-OprM is recognized as a major cause of resistance to aminoglycosides, fluoroquinolones, and zwitterionic cephalosporins in Pseudomonas aeruginosa. In this study, 57 clonally unrelated strains recovered from non-cystic fibrosis patients were analyzed to characterize the mutations resulting in upregulation of the mexXY operon. Forty-four (77.2%) of the strains, classified as agrZ mutants were found to harbor mutations inactivating the local repressor gene (mexZ) of the mexXY operon (n = 33; 57.9%) or introducing amino acid substitutions in its product, MexZ (n = 11; 19.3%). These sequence variations, which mapped in the dimerization domain, the DNA binding domain, or the rest of the MexZ structure, mostly affected amino acid positions conserved in TetR-like regulators. The 13 remaining MexXY-OprM strains (22.8%) contained intact mexZ genes encoding wild-type MexZ proteins. Eight (14.0%) of these isolates, classified as agrW1 mutants, overexpressed the gene PA5471, which codes for the MexZ antirepressor ArmZ [corrected], with 5 strains exhibiting growth defects at 37°C and 44°C, consistent with mutations impairing ribosome activity. Interestingly, one agrW1 mutant appeared to harbor a 7-bp deletion in the coding sequence of the leader peptide, PA5471.1, involved in ribosome-dependent, translational attenuation of PA5471 expression. Finally, DNA sequencing and complementation experiments revealed that 5 (8.8%) strains, classified as agrW2 mutants, harbored single amino acid variations in the sensor histidine kinase of ParRS, a two-component system known to positively control mexXY expression. Collectively, these results demonstrate that clinical strains of P. aeruginosa exploit different regulatory circuitries to mutationally overproduce the MexXY-OprM pump and become multidrug resistant, which accounts for the high prevalence of MexXY-OprM mutants in the clinical setting.
authors.affiliation: Centre National de Référence de la Résistance aux Antibiotiques, Centre Hospitalier Régional Universitaire de Besançon, Université de Franche-Comté, Besançon, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Guénard
authors.forename: Cédric
authors.initials: C
authors.lastname: Muller
authors.forename: Laura
authors.initials: L
authors.lastname: Monlezun
authors.forename: Philippe
authors.initials: P
authors.lastname: Benas
authors.forename: Isabelle
authors.initials: I
authors.lastname: Broutin
authors.forename: Katy
authors.initials: K
authors.lastname: Jeannot
authors.forename: Patrick
authors.initials: P
authors.lastname: Plésiat
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009876:Operon / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics
chemical_list: D000617:Aminoglycosides; D001426:Bacterial Proteins