title: Copy Number Change of the NDM-1 sequence in a multidrug-resistant Klebsiella pneumoniae clinical isolate.
abstract: The genetic features of the antimicrobial resistance of a multidrug resistant Klebsiella pneumoniae strain harboring bla NDM-1 were investigated to increase our understanding of the evolution of NDM-1. The strain, KPX, came from a Taiwanese patient with a hospitalization history in New Delhi. Complete DNA sequencing was performed; and the genes responsible for antimicrobial resistance were systematically examined and isolated by library screening. KPX harbored two resistance plasmids, pKPX-1 and pKPX-2, which are 250-kb and 141-kb in size, respectively, with bla NDM-1 present on pKPX-1. The plasmid pKPX-1 contained genes associated with the IncR and IncF groups, while pKPX-2 belonged to the IncF family. Each plasmid carried multiple antimicrobial resistance genetic determinants. The gene responsible for resistance to carbapenems was found on pKPX-1 and that for resistance to aztreonam was found on pKPX-2. To our surprise, we discovered that bla NDM-1 exists on pKPX-1 as multiple copies in the form of tandem repeats. Amplification of bla NDM-1 was found to occur by duplication of an 8.6-kb unit, with the copy number of the repeat varying from colony to colony. This repeat sequence is identical to that of the pNDM-MAR except for two base substitutions. The copy number of bla NDM-1 of colonies under different conditions was assessed by Southern blotting and quantitative PCR. The bla NDM-1 sequence was maintained in the presence of the antimicrobial selection; however, removal of antimicrobial selection led to the emergence of susceptible bacterial populations with a reduced copy number or even the complete loss of the bla NDM-1 sequence. The dynamic nature of the NDM-1 sequence provides a strong argument for judicious use of the broad-spectrum antimicrobials in order to reduce the development and spread of antimicrobial resistance among pathogens.
authors: Institute of Molecular and Genomic Medicine, National Health Research Institutes, Miaoli, Taiwan.
authors: Tzu-Wen
authors: TW
authors: Huang
authors: Te-Li
authors: TL
authors: Chen
authors: Ying-Tsong
authors: YT
authors: Chen
authors: Tsai-Ling
authors: TL
authors: Lauderdale
authors: Tsai-Lien
authors: TL
authors: Liao
authors: Yi-Tzu
authors: YT
authors: Lee
authors: Chien-Pei
authors: CP
authors: Chen
authors: Yen-Ming
authors: YM
authors: Liu
authors: Ann-Chi
authors: AC
authors: Lin
authors: Ya-Hui
authors: YH
authors: Chang
authors: Keh-Ming
authors: KM
authors: Wu
authors: Ralph
authors: R
authors: Kirby
authors: Jui-Fen
authors: JF
authors: Lai
authors: Mei-Chen
authors: MC
authors: Tan
authors: Leung-Kei
authors: LK
authors: Siu
authors: Chung-Ming
authors: CM
authors: Chang
authors: Chang-Phone
authors: CP
authors: Fung
authors: Shih-Feng
authors: SF
authors: Tsai
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D015780:Carbapenems / Q000494:pharmacology; D015169:Colony Count, Microbial; D056915:DNA Copy Number Variations; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics*; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D007710:Klebsiella Infections / Q000188:drug therapy / Q000382:microbiology; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D008297:Male; D010957:Plasmids / Q000737:chemistry*; D017422:Sequence Analysis, DNA; D020080:Tandem Repeat Sequences; D001618:beta-Lactamases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D015780:Carbapenems; D004269:DNA, Bacterial; D001618:beta-Lactamases; C552864:beta-lactamase NDM-1
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