title: Carbapenem resistance mechanisms in Pseudomonas aeruginosa: alterations of porin OprD and efflux proteins do not fully explain resistance patterns observed in clinical isolates.
abstract: Imipenem resistance in Pseudomonas aeruginosa is considered to be associated with loss of the porin OprD combined with activity of chromosomal beta-lactamase (AmpC), while overexpression of multidrug efflux pumps is considered to confer meropenem resistance. Carbapenem resistance can also result from production of metallo-beta-lactamases. Transcription of oprD and efflux pump genes mexB, mexY and mexF was analysed in 23 clinical isolates of P. aeruginosa by quantitative RT-PCR. oprD was sequenced in all, and mexR, regulator of efflux pump MexAB-OprM, in selected isolates. Four isolates that were imipenem susceptible had significant reduction of oprD mRNA and presence of oprD mutations causing frameshift or translational stop. In strains only resistant to imipenem no significant difference in transcription of oprD was observed between low-level and high-level resistant isolates. The differences could not be explained by either pattern of oprD mutations. Increased transcription of mexB generally correlated well with meropenem resistance. One high-level meropenem-resistant isolate showed no significant change in mexB mRNA, but sequencing confirmed presence of a nalB mutation. Furthermore, one meropenem-susceptible isolate showed significant increase in mexB transcription, but no mexR mutations. In summary, our findings indicate that the resistance patterns observed cannot be fully explained by the currently described carbapenem resistance mechanisms.
authors.affiliation: Division of Clinical Bacteriology, Department of Laboratory Medicine, Karolinska Institute, Karolinska University Hospital, SE-17176 Stockholm, Sweden.
authors.forename: Nagwa
authors.initials: N
authors.lastname: El Amin
authors.forename: Christian G
authors.initials: CG
authors.lastname: Giske
authors.forename: Shah
authors.initials: S
authors.lastname: Jalal
authors.forename: Berit
authors.initials: B
authors.lastname: Keijser
authors.forename: Göran
authors.initials: G
authors.lastname: Kronvall
authors.forename: Bengt
authors.initials: B
authors.lastname: Wretlind
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D015780:Carbapenems / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D015378:Imipenem / Q000494:pharmacology / Q000627:therapeutic use; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology; D000077731:Meropenem; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics* / Q000502:physiology; D009154:Mutation / Q000235:genetics; D018272:Porins / Q000235:genetics* / Q000502:physiology; D011552:Pseudomonas Infections / Q000188:drug therapy; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013845:Thienamycins / Q000494:pharmacology / Q000627:therapeutic use; D014158:Transcription, Genetic; D018440:beta-Lactam Resistance / Q000235:genetics
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D015780:Carbapenems; D015378:Imipenem; D026901:Membrane Transport Proteins; D000077731:Meropenem; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D018272:Porins; D012333:RNA, Messenger; D012097:Repressor Proteins; D013845:Thienamycins; C118597:MexB protein, Pseudomonas aeruginosa; C423620:MexR protein, Pseudomonas aeruginosa; C402791:MexXY protein, Pseudomonas aeruginosa; C077157:OprD protein, Pseudomonas aeruginosa