High Prevalence of blaNDM Variants Among Carbapenem-Resistant Escherichia coli in Northern Jiangsu Province, China

Abstract

The continuous emergence of carbapenem-resistant <i>Escherichia coli</i> (CRECO) presents a great challenge to public health. New Delhi metallo-lactamase (NDM) variants are widely disseminated in China, so the research on the prevalence and transmission of diverse <i>bla</i> _NDM variants is urgently needed. In the present study, 54 CRECO isolates were collected from 1,185 <i>Escherichia coli</i> isolates in five hospitals in Northern Jiangsu Province, China from September 2015 to August 2016. Antimicrobial susceptibility tests, PCR detection of resistance determinants, multi-locus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were performed to characterize these strains. Plasmid conjugation experiments were carried out to determine the transferability of resistant genes from selected isolates. PCR-based replicon typing (PBRT), S1 nuclease-PFGE, and Southern blotting were conducted for plasmid profiling. Carbapenemase genes were detectable in all CRECO isolates, among which thirty-one CRECO isolates were found to carry <i>bla</i> _NDM-5 (54.7%), while, <i>bla</i> _NDM-1, <i>bla</i> _NDM-7, <i>bla</i> _NDM-4, <i>bla</i> _NDM-9, and <i>bla</i> _KPC-2 were identified in 14, five, two, one, and one isolates, respectively. MLST results revealed 15 different STs and four new STs were first reported to be linked with NDM-producing isolates. PFGE typing showed that no more than two isolates with the same ST appeared to the same band pattern except three ST410 isolates. Twenty-six selected NDM-producing isolates were successfully transferred to <i>E. coli</i> J53 by conjugation experiments. Notably, 50.0% (13/26) of <i>bl</i>a_NDM variants were found to be carried by ~55 kb IncX3 plasmid. Our study reported a high prevalence of <i>bl</i>a_NDM variants, especially <i>bla</i> _NDM-5, in Northern Jiangsu province, China. Diverse <i>bla</i> _NDM variants were mainly carried by ~55 kb IncX3 plasmids, suggesting that the fast evolution and high transferability of this kind of plasmid promote the high prevalence of <i>bla</i> _NDM variants. Therefore, large-scale surveillance and effective infection control measures are also urgently needed to prevent diverse <i>bla</i> _NDM variants from becoming epidemic in the future.