title: An Increase in the clinical isolation of acquired AmpC β-lactamase-producing Klebsiella pneumoniae in Korea from 2007 to 2010.
abstract: We investigated the occurrence and genetic basis of AmpC β-lactamase (AmpC)-mediated antibiotic resistance, by examining Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis isolates at a university hospital, from 2007 to 2010. The ampC genes were detected by multiplex AmpC PCR, and AmpC-positive strains were subjected to DNA sequencing. Extended-spectrum β-lactamase (ESBL) production was assessed using the ESBL disk test based on the utilization of boronic acid. Carbapenem-resistant isolates were further investigated by the modified Hodge test, a carbapenemase inhibition test and SDS-PAGE experiments. AmpC expression was detected in 1.6% of E. coli (39 DHA-1, 45 CMY-2, and 1 CMY-1) isolates, 7.2% of K. pneumoniae (39 DHA-1, 45 CMY-2, and 1 CMY-1) isolates, and 2.5% of P. mirabilis (8 CMY-2 and 1 CMY-1) isolates. Of the 198 acquired AmpC producers, 58 isolates (29.3%) also produced an ESBL enzyme. Among the acquired AmpC-producing K. pneumoniae isolates, the minimum inhibitory concentration (MIC) MIC50/MIC90 values for cefoxitin, cefotaxime, cefepime, imipenem, and meropenem were >32/>32, 16/>32, 1/16, 0.25/0.5, and <0.125/0.125 µg/mL, respectively. The MIC values for carbapenem were ≥2 µg/mL for 2 K. pneumoniae isolates, both of which carried the bla DHA-1 gene with a loss of OmpK36 expression, but were negative for carbapenemase production. The acquisition of AmpC-mediated resistance in K. pneumoniae isolates increased, as did the proportion of AmpC and ESBL co-producers among the hospital isolates. The accurate identification of isolates producing AmpCs and ESBLs may aid in infection control and will assist physicians in selecting an appropriate antibiotic regimen.
authors.affiliation: Department of Laboratory Medicine, Hallym University College of Medicine, Chuncheon, Korea.
authors.forename: Min-Jeong
authors.initials: MJ
authors.lastname: Park
authors.forename: Taek-Kyung
authors.initials: TK
authors.lastname: Kim
authors.forename: Wonkeun
authors.initials: W
authors.lastname: Song
authors.forename: Jae-Seok
authors.initials: JS
authors.lastname: Kim
authors.forename: Han-Sung
authors.initials: HS
authors.lastname: Kim
authors.forename: Jacob
authors.initials: J
authors.lastname: Lee
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D004756:Enterobacteriaceae Infections / Q000453:epidemiology* / Q000382:microbiology*; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology / Q000302:isolation & purification; D006785:Hospitals, University / Q000706:statistics & numerical data; D006801:Humans; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology / Q000302:isolation & purification / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D060885:Multiplex Polymerase Chain Reaction; D011513:Proteus mirabilis / Q000187:drug effects / Q000201:enzymology / Q000302:isolation & purification; D056910:Republic of Korea / Q000453:epidemiology; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C048795:AmpC beta-lactamases; D001618:beta-Lactamases
keywords: AmpC β-lactamases; CMY-2; DHA-1; Klebsiella pneumoniae