Genetic characteristics of blaNDM-1-positive plasmid in Citrobacterfreundii isolate separated from a clinical infectious patient

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This study reports an infectious case involving an NDM-1-producing Citrobacterfreundii and further explored the potential threat of the blaNDM-1 gene by analysing the characteristics of the NDM-1-encoding plasmid sequence. A blaNDM-1-positive C. freundii with high resistance to carbapenems was separated from a clinical patient suffering from a urinary tract infection. S1 nuclease-based plasmid analysis followed by Southern blot hybridization, a conjugation experiment and electrotransformation confirmed that the blaNDM-1 gene was located on a plasmid. High-throughput sequencing of the blaNDM-1-postive plasmid (pCFNDM-CN) showed that it was a 54 kb IncX-type plasmid and contained a backbone region and a variable region with two β-lactamase genes (blaNDM-1 and blaSHV-12). The NDM-1 composite transposon in the variable region was surrounded by IS26 and IS5-truncated ISAba125, and shared a high sequence similarity to the blaNDM-1 surrounding structure in Acinetobacter spp. Our research suggested that the NDM-1 composite transposon might play an essential role in mobilization of the blaNDM-1 gene from Acinetobacter spp. to Enterobacteriaceae.

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