High prevalence of non-clonal imipenem-nonsusceptible Enterobacter spp. isolates in Korea and their association with porin down-regulation.
We investigated the prevalence and clonal distribution of imipenem-nonsusceptible Enterobacter clinical isolates from hospitals in Korea and the contributions of various mechanisms to imipenem nonsusceptibility. The in vitro antimicrobial susceptibility to imipenem of 357 non-duplicated Enterobacter isolates obtained from eight geographically distant tertiary care hospitals in Korea was evaluated. Imipenem-nonsusceptible Enterobacter isolates were genotyped. Additionally, β-lactamase genes were screened using PCR, and the expression of efflux pump and porin genes was investigated using quantitative RT-PCR. A total of 31 isolates (8.7%) were not susceptible to imipenem. Clonal diversity of 17 imipenem-nonsusceptible E. cloacae isolates was demonstrated by multilocus sequence typing. Fourteen imipenem-nonsusceptible E. aerogenes isolates were found to be distantly genetically related by an ERIC-PCR analysis. Expression levels of porin ompD and ompK35 genes were decreased in all imipenem-nonsusceptible E. cloacae and E. aerogenes isolates. However, only two isolates were found positive for blaIMPand blaVIMgenes, and expression of the efflux pump gene, acrB, was not associated with reduced imipenem susceptibility. Imipenem resistance seems to have occurred independently in most of the imipenem-nonsusceptible isolates in this study, and decreased porin expression was found to be the main mechanism underlying this reduced susceptibility to imipenem.
Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon 16419, South Korea.
Ji-Young
JY
Lee
Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon 16419, South Korea.
Yoon-Kyoung
YK
Hong
Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon 16419, South Korea.
Haejeong
H
Lee
Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon 16419, South Korea. Electronic address: ksko@skku.edu.
Kwan Soo
KS
Ko
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015536:Down-Regulation; D004754:Enterobacter / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D004756:Enterobacteriaceae Infections / Q000453:epidemiology / Q000382:microbiology*; D005838:Genotype; D006801:Humans; D015378:Imipenem / Q000494:pharmacology*; D058889:Molecular Typing; D018272:Porins / Q000096:biosynthesis*; D015995:Prevalence; D060888:Real-Time Polymerase Chain Reaction; D056910:Republic of Korea / Q000453:epidemiology; D062606:Tertiary Care Centers; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics
D000900:Anti-Bacterial Agents; D018272:Porins; D015378:Imipenem; D001618:beta-Lactamases
Enterobacter aerogenes; Enterobacter cloacae; Imipenem; Porin