New Delhi Metallo-Beta-Lactamase-Producing Enterobacteriaceae in South Korea Between 2010 and 2015

Abstract

This study was carried out to investigate the epidemiological time-course of New Delhi metallo-beta-lactamase- (NDM-) mediated carbapenem resistance in Enterobacteriaceae in South Korea. A total of 146 non-duplicate NDM-producing Enterobacteriaceae recovered between 2010 and 2015 were voluntarily collected from 33 general hospitals and confirmed by PCR. The species were identified by sequences of the 16S rDNA. Antimicrobial susceptibility was determined either by the disk diffusion method or by broth microdilution, and the carbapenem MICs were determined by agar dilution. Then, multilocus sequence typing and PCR-based replicon typing was carried out. Co-carried genes for drug resistance were identified by PCR and sequencing. The entire genomes of eight random selected NDM producers were sequenced. A total of 69 Klebsiella pneumoniae of 12 sequence types (STs), 34 Escherichia coli of 15 STs, 28 Enterobacter spp. (including one Enterobacter aerogenes), nine Citrobacter freundii, four Raoultella spp., and two Klebsiella oxytoca isolates produced either NDM-1 (n = 126), NDM-5 (n = 18), or NDM-7 (n = 2). The isolates co-produced CTX-M-type ESBL (52.1%), AmpCs (27.4%), additional carbapenemases (7.1%), and/or 16S rRNA methyltransferases (4.8%), resulting in multidrug-resistance (47.9%) or extensively drug-resistance (52.1%). Among plasmids harboring bla_NDM, IncX3 was predominant (77.4%), followed by the IncFII type (5.8%). Genome analysis revealed inter-species and inter-strain horizontal gene transfer of the plasmid. Both clonal dissemination and plasmid transfer contributed to the wide dissemination of NDM producers in South Korea.

Keywords: IncFII; IncX3; New Delhi metallo-beta-lactamase; Tn125; carbapenemase-producing Enterobacteriaceae.

Figure 1

Schematic representation of the bla_NDM-harboring IncX3 and IncFII plasmids. Name of the plasmids and the size in parenthesis are denoted for the plasmids, and the district of isolation are indicated on the map of Korean peninsula in front of the plasmid name. Name of the plasmids from E. coli are indicated in black, from Enterobacter spp. in blue, and from K. pneumoniae in red. Open arrows indicate coding sequences for conjugal transfer (light green), drug resistance (red), replication origin (blue), toxin/antitoxin system (black), transposase (yellow), and integrase (green). Insertion sequences are indicated in yellow boxes. The Tn125 is marked with a red-bordered open box, and the class 1 integron is indicated with a green-bordered open box. Genetic variants of each plasmid referred by pCREC-629_3 are indicated on the right side of the schematic representation of the plasmid for locating the point of substitution: arrowheads, deletion; square bracket, insertion. Together with the nt substitutions, details of insertion are indicated with +, and that of deletion with Δ in the end of the schematic presentation of the plasmid.