Molecular characterization of NDM-1-producing carbapenem-resistant E. cloacae complex from a tertiary hospital in Chongqing, China
Kewang Hu, Jisheng Zhang, Jingbo Zou, Lingyi Zeng, Jie Li, Jianmin Wang, Wenzhang Long, Xiaoli Zhang
Abstract
Background The aim of this study was to clarify the molecular characterization of NDM-1-producing carbapenem-resistant Enterobacter cloacae complex (CREL) at a teaching hospital in Chongqing, China. Methods 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 bla NDM-1 - and mcr-9 -carrying plasmids was analyzed. Results A total of 10 bla NDM-1 -positive CREL isolates were identified. All isolates harbored multiple resistance genes. ECL68 and ECL78 co-produce bla NDM-1 and mcr-9 . 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 bla NDM-1 or mcr-9 could be transferred to the recipient Escherichia coli . WGS indicated that bla NDM-1 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 ( repAB ), partitioning ( parABM ), and conjugation/type IV secretion ( tra/virB ). Analysis of the genetic environment showed that bla NDM-1 in three plasmids exhibited a highly similar structure to protype Tn 125 . Co-existence of bla NDM-1 and the colistin resistance gene mcr-9 was detected in the two isolates, ECL68 and ECL78. In ECL68, bla NDM-1 and mcr-9 were present on the same plasmid while located in two separate plasmids in ECL78. The genetic environment of mcr-9 was organized as IS 26-wbuC-mcr-9- IS 903-pcoS-pcoE-rcnA-rcnR , and the two-component system encoding genes qseC and qseB was not found in two plasmids, which could explain mcr-9 -harboring strains’ colistin susceptibility. Conclusions We first report a nosocomial outbreak of NDM-1-producing E. cloacae complex ST177 in China. Conjugative plasmids contributed to the horizontal transfer of antibiotic resistance genes. The prevalence and even coexistence of bla NDM-1 and mcr-9 may further threaten public health. Our results highlight further surveillance for bla NDM-1 , and mcr-9 is essential to prevent its dissemination.