title: The MexA-MexB-OprM multidrug efflux system of Pseudomonas aeruginosa is growth-phase regulated.
abstract: Intrinsic antibiotic resistance in Pseudomonas aeruginosa is attributed to low outer membrane permeability and drug efflux mediated by the products of mexAmexBoprM efflux operon. Using a mexA-phoA fusion, expression of the efflux genes was assessed as a function of growth in a variety of strains. The efflux operon was growth-phase regulated in both wild-type and nalB strains, being minimally expressed in lag phase and increasing in log to late log phase. MexR, the only known regulator of MexAMexBOprM and target of mutation in nalB strains, was not involved in the growth-phase regulation. The las cascade regulates genes based on increased cell-density, but a deletion in lasR had no effect on mexAmexBoprM expression. Putative recognition sequences for AlgT/U and RpoN were identified upstream of mexA, but algT/U and rpoN null mutants also had no effect on mexAmexBoprM expression.
authors.affiliation: Department of Microbiology and Immunology, Queen's University, Kingston, Ont., Canada.
authors.forename: K
authors.initials: K
authors.lastname: Evans
authors.forename: K
authors.initials: K
authors.lastname: Poole
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D004352:Drug Resistance, Microbial / Q000235:genetics*; D018432:Drug Resistance, Multiple / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D026901:Membrane Transport Proteins; D009876:Operon / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D026901:Membrane Transport Proteins; C118598:MexA protein, Pseudomonas aeruginosa; C118597:MexB protein, Pseudomonas aeruginosa