title: Polymyxin Susceptibility in Pseudomonas aeruginosa Linked to the MexXY-OprM Multidrug Efflux System.
abstract: The ribosome-targeting antimicrobial, spectinomycin (SPC), strongly induced the mexXY genes of the MexXY-OprM multidrug efflux system in Pseudomonas aeruginosa and increased susceptibility to the polycationic antimicrobials polymyxin B and polymyxin E, concomitant with a decrease in expression of the polymyxin resistance-promoting lipopolysaccharide (LPS) modification loci, arnBCADTEF and PA4773-74. Consistent with the SPC-promoted reduction in arn and PA4773-74 expression being linked to mexXY, expression of these LPS modification loci was moderated in a mutant constitutively expressing mexXY and enhanced in a mutant lacking the efflux genes. Still, the SPC-mediated increase in polymyxin susceptibility was retained in mutants lacking arnB and/or PA4773-74, an indication that their reduced expression in SPC-treated cells does not explain the enhanced polymyxin susceptibility. That the polymyxin susceptibility of a mutant strain lacking mexXY was unaffected by SPC exposure, however, was an indication that the unknown polymyxin resistance 'mechanism' is also influenced by the MexXY status of the cell. In agreement with SPC and MexXY influencing polymyxin susceptibility as a result of changes in the LPS target of these agents, SPC treatment yielded a decline in common polysaccharide antigen (CPA) synthesis in wild-type P. aeruginosa but not in the ΔmexXY mutant. A mutant lacking CPA still showed the SPC-mediated decline in polymyxin MICs, however, indicating that the loss of CPA did not explain the SPC-mediated MexXY-dependent increase in polymyxin susceptibility. It is possible, therefore, that some additional change in LPS promoted by SPC-induced mexXY expression impacted CPA synthesis or its incorporation into LPS and that this was responsible for the observed changes in polymyxin susceptibility.
authors.affiliation: Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada poolek@queensu.ca.
authors.forename: Keith
authors.initials: K
authors.lastname: Poole
authors.affiliation: Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.
authors.forename: Calvin Ho-Fung
authors.initials: CH
authors.lastname: Lau
authors.affiliation: Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.
authors.forename: Christie
authors.initials: C
authors.lastname: Gilmour
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Youai
authors.initials: Y
authors.lastname: Hao
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.
authors.forename: Joseph S
authors.identifier: http://orcid.org/0000-0002-1822-1165
authors.initials: JS
authors.lastname: Lam
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D003091:Colistin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D056426:Genetic Loci; D008070:Lipopolysaccharides / Q000096:biosynthesis / Q000235:genetics; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011112:Polymyxin B / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D000198:Spectinomycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D008070:Lipopolysaccharides; D026901:Membrane Transport Proteins; C402791:MexXY protein, Pseudomonas aeruginosa; C402263:OprM protein, Pseudomonas aeruginosa; D000198:Spectinomycin; D011112:Polymyxin B; D003091:Colistin