title: [Carbapenem resistance in Pseudomonas aeruginosa isolates: an example of interaction between different mechanisms].
abstract: OBJECTIVE
  To identify the outer membrane protein absent in the resistant isolates and to determine both the causes of its absence in the membrane and the presence of other mechanisms of carbapenem resistance in clinical isolates of Pseudomonas aeruginosa.
  
  
  METHODS
  Twenty isolates from an outbreak of P. aeruginosa previously characterized as metallo-beta-lactamase IMP-13 producers were studied. All the isolates exhibited equal expression of the IMP-13 enzyme, but only five of them were carbapenem-resistant. It was found that the five resistant isolates lacked a outer membrane protein. The oprD and ampC genes were sequenced; the outer membrane proteins were identified using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry; the OprD and AmpC expressions, as well as the Mex efflux system, were assessed by real-time polymerase chain reaction; and finally, the contribution of reduced OprD to carbapenem resistance was determined.
  
  
  RESULTS
  The absent outer membrane protein in group R was identified as OprD-TS; however, no variations in its expression were observed. The oprD gene presented mutations in the five resistant isolates. The production of AmpC PDC-5-type enzyme and the MexAB-OprM efflux system was the same in both carbapenem-sensitive and -resistant isolates. The contribution of the combined presence of IMP-13 and reduced OprD to increased resistance was examined.
  
  
  CONCLUSIONS
  Different mechanisms contribute to carbapenem resistance in IMP-13-producing isolates. The possibility that these IMP-13-producing isolates could go undetected poses a latent risk when selecting mutants with added resistance mechanisms in order to enhance carbapenem resistance.
authors.affiliation: Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Argentina.
authors.forename: Gisela
authors.initials: G
authors.lastname: Santella
authors.forename: Simona
authors.initials: S
authors.lastname: Pollini
authors.forename: Jean-Denis
authors.initials: JD
authors.lastname: Docquier
authors.forename: Marisa
authors.initials: M
authors.lastname: Almuzara
authors.forename: Gabriel
authors.initials: G
authors.lastname: Gutkind
authors.forename: Gian Maria
authors.initials: GM
authors.lastname: Rossolini
authors.forename: Marcela
authors.initials: M
authors.lastname: Radice
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D015780:Carbapenems / Q000494:pharmacology*; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics / Q000502:physiology*; D016521:Electrophoresis, Gel, Pulsed-Field; D005798:Genes, Bacterial; D006801:Humans; D015378:Imipenem / Q000378:metabolism / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology; D000077731:Meropenem; D009154:Mutation; D018272:Porins / Q000172:deficiency / Q000235:genetics* / Q000502:physiology; D011552:Pseudomonas Infections / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D012189:Retrospective Studies; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013845:Thienamycins / Q000378:metabolism / Q000494:pharmacology; D018440:beta-Lactam Resistance / Q000235:genetics / Q000502:physiology*; D001618:beta-Lactamases / Q000235:genetics / Q000502:physiology*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D015780:Carbapenems; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; C402263:OprM protein, Pseudomonas aeruginosa; D018272:Porins; D013845:Thienamycins; C077157:OprD protein, Pseudomonas aeruginosa; D015378:Imipenem; C048795:AmpC beta-lactamases; C573532:IMP-13 beta-lactamase, Pseudomonas aeruginosa; D001618:beta-Lactamases; C063912:carbapenemase; D000077731:Meropenem