AUTHOR=Hu Kewang , Zhang Jisheng , Zou Jingbo , Zeng Lingyi , Li Jie , Wang Jianmin , Long Wenzhang , Zhang Xiaoli 

TITLE=Molecular characterization of NDM-1-producing carbapenem-resistant E. cloacae complex from a tertiary hospital in Chongqing, China

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2022.935165

DOI=10.3389/fcimb.2022.935165

ISSN=2235-2988

ABSTRACT=<sec><title>Background</title><p>The aim of this study was to clarify the molecular characterization of NDM-1-producing carbapenem-resistant <italic>Enterobacter cloacae </italic>complex (CREL) at a teaching hospital in Chongqing, China.</p></sec><sec><title>Methods</title><p>Antimicrobial susceptibility and resistance genes were analyzed. Epidemiological relationship was analyzed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Conjugation experiments were performed to determine the transferability of plasmids. Whole-genome sequencing (WGS) of strains was implemented, and the genetic environment of the <italic>bla</italic><sub>NDM-1</sub>- and <italic>mcr-9</italic>-carrying plasmids was analyzed.</p></sec><sec><title>Results</title><p>A total of 10 <italic>bla</italic><sub>NDM-1</sub>-positive CREL isolates were identified. All isolates harbored multiple resistance genes. ECL68 and ECL78 co-produce <italic>bla</italic><sub>NDM-1</sub> and <italic>mcr-9</italic>. Among the four different sequence types (STs) detected, ST1466 was assigned as a novel ST. Six isolates exhibited highly similar PFGE patterns. Conjugation assay proved that all plasmids containing <italic>bla</italic><sub>NDM-1</sub> or <italic>mcr-9</italic> could be transferred to the recipient <italic>Escherichia coli</italic>. WGS indicated that <italic>bla</italic><sub>NDM-1</sub> genes were carried by diverse plasmids, including IncHI2/IncN, IncX3, and one unclassified plasmid type. The backbone structure of these plasmids is involved in replication initiation (<italic>repAB</italic>), partitioning (<italic>parABM</italic>), and conjugation/type IV secretion (<italic>tra/virB</italic>). Analysis of the genetic environment showed that <italic>bla</italic><sub>NDM-1</sub> in three plasmids exhibited a highly similar structure to protype Tn<italic>125</italic>. Co-existence of <italic>bla</italic><sub>NDM-1</sub> and the colistin resistance gene <italic>mcr-9</italic> was detected in the two isolates, ECL68 and ECL78. In ECL68, <italic>bla</italic><sub>NDM-1</sub> and <italic>mcr-9</italic> were present on the same plasmid while located in two separate plasmids in ECL78. The genetic environment of <italic>mcr-9</italic> was organized as IS<italic>26-wbuC-mcr-9-</italic>IS<italic>903-pcoS-pcoE-rcnA-rcnR</italic>, and the two-component system encoding genes <italic>qseC</italic> and <italic>qseB</italic> was not found in two plasmids, which could explain <italic>mcr-9</italic>-harboring strains’ colistin susceptibility.</p></sec><sec><title>Conclusions</title><p>We first report a nosocomial outbreak of NDM-1-producing <italic>E. cloacae complex</italic> ST177 in China. Conjugative plasmids contributed to the horizontal transfer of antibiotic resistance genes. The prevalence and even coexistence of <italic>bla</italic><sub>NDM-1</sub> and <italic>mcr-9</italic> may further threaten public health. Our results highlight further surveillance for <italic>bla</italic><sub>NDM-1</sub>, and <italic>mcr-9</italic> is essential to prevent its dissemination.</p></sec>