title: Reduced imipenem susceptibility in Klebsiella pneumoniae clinical isolates with plasmid-mediated CMY-2 and DHA-1 beta-lactamases co-mediated by porin loss.
abstract: We investigated the resistance mechanisms and clonality among 42 imipenem-non-susceptible Klebsiella pneumoniae isolated at a tertiary care hospital in Korea. Two isolates had bla(VIM-2) alleles, whereas bla(CMY-2)- and bla(DHA-1)-like alleles were detected in 24 and 16 isolates, respectively, with these enzymes confirmed by sequencing for representative isolates. Transfer of bla(CMY-2) and bla(DHA-1) was achieved by conjugation. Addition of 300 mg/L 3-aminophenylboronic acid (APB) reduced the minimum inhibitory concentration for 90% of the organisms (MIC(90)) of imipenem and meropenem eight- and four-fold, respectively, for the bla(CMY-2)- and bla(DHA-1)-positive isolates, confirming the role of these enzymes in resistance. SDS-PAGE of outer membrane proteins for representative isolates showed lack or greatly diminished expression of OmpK35 and OmpK36 porins. Pulsed-field gel electrophoresis of XbaI-restricted genomic DNA revealed two closely related clusters among 23 bla(CMY-2)-positive isolates, whereas those with bla(DHA-1) were more heterogeneous. In conclusion, reduced imipenem susceptibility among K. pneumoniae at this Korean hospital was largely co-mediated by production of plasmid-mediated AmpC beta-lactamases along with lack or greatly diminished expression of OmpK35 and OmpK36 porins.
authors.affiliation: Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul 120-752, South Korea.
authors.forename: Kyungwon
authors.initials: K
authors.lastname: Lee
authors.forename: Dongeun
authors.initials: D
authors.lastname: Yong
authors.forename: Yeong Seon
authors.initials: YS
authors.lastname: Choi
authors.forename: Jong Hwa
authors.initials: JH
authors.lastname: Yum
authors.forename: June Myung
authors.initials: JM
authors.lastname: Kim
authors.forename: Neil
authors.initials: N
authors.lastname: Woodford
authors.forename: David M
authors.initials: DM
authors.lastname: Livermore
authors.forename: Yunsop
authors.initials: Y
authors.lastname: Chong
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis; D001426:Bacterial Proteins / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D015378:Imipenem / Q000494:pharmacology*; D007525:Isoelectric Focusing; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D008826:Microbial Sensitivity Tests; D010957:Plasmids; D018272:Porins / Q000032:analysis / Q000502:physiology*; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D018272:Porins; D015378:Imipenem; C103022:beta-lactamase CMY-2; C048795:AmpC beta-lactamases; D001618:beta-Lactamases