title: Efflux unbalance in Pseudomonas aeruginosa isolates from cystic fibrosis patients.
abstract: Retrospective analysis of 189 nonredundant strains of Pseudomonas aeruginosa sequentially recovered from the sputum samples of 46 cystic fibrosis (CF) patients over a 10-year period (1998 to 2007) revealed that 53 out of 189 (28%) samples were hypersusceptible to the beta-lactam antibiotic ticarcillin (MIC < or = 4 microg/ml) (phenotype dubbed Tic(hs)). As evidenced by trans-complementation and gene inactivation experiments, the mutational upregulation of the efflux system MexXY was responsible for various degrees of resistance to aminoglycosides in a selection of 11 genotypically distinct strains (gentamicin MICs from 2 to 64 microg/ml). By demonstrating for the first time that the MexXY pump may evolve in CF strains, we found that a mutation leading to an F1018L change in the resistance-nodulation-cell division (RND) transporter MexY was able to increase pump-promoted resistance to aminoglycosides, cefepime, and fluoroquinolones twofold. The inactivation of the mexB gene (which codes for the RND transporter MexB) in the 11 selected strains showed that the Tic(hs) phenotype was due to a mutational or functional loss of function of MexAB-OprM, the multidrug efflux system known to contribute to the natural resistance of P. aeruginosa to beta-lactams (e.g., ticarcillin and aztreonam), fluoroquinolones, tetracycline, and novobiocin. Two of the selected strains synthesized abnormally low amounts of the MexB protein, and 3 of 11 strains expressed truncated MexB (n = 2) or MexA (n = 1) polypeptide as a result of mutations in the corresponding genes, while 7 of 11 strains produced wild-type though nonfunctional MexAB-OprM pumps at levels similar to or even higher than that of reference strain PAO1. Overall, our data indicate that while MexXY is necessary for P. aeruginosa to adapt to the hostile environment of the CF lung, the MexAB-OprM pump is dispensable and tends to be lost or inactivated in subpopulations of P. aeruginosa.
authors.affiliation: Department of Bacteriology, University of Franche-Comté, Faculty of Medicine, F-25030 Besançon, France.
authors.forename: Lucie
authors.initials: L
authors.lastname: Vettoretti
authors.forename: Patrick
authors.initials: P
authors.lastname: Plésiat
authors.forename: Cédric
authors.initials: C
authors.lastname: Muller
authors.forename: Farid
authors.initials: F
authors.lastname: El Garch
authors.forename: Gilles
authors.initials: G
authors.lastname: Phan
authors.forename: Inna
authors.initials: I
authors.lastname: Attrée
authors.forename: Arnaud
authors.initials: A
authors.lastname: Ducruix
authors.forename: Catherine
authors.initials: C
authors.lastname: Llanes
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003550:Cystic Fibrosis / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011552:Pseudomonas Infections / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D013183:Sputum / Q000382:microbiology; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; C402791:MexXY protein, Pseudomonas aeruginosa; C402263:OprM protein, Pseudomonas aeruginosa; D047090:beta-Lactams