Dissemination of NDM-1-Producing Enterobacteriaceae Mediated by the IncX3-Type Plasmid

The emergence and spread of NDM-1-producing Enterobacteriaceae have resulted in a worldwide public health risk that has affected some provinces of China. China is an exceptionally large country, and there is a crucial need to investigate the epidemic of bla (NDM-1)-positive Enterobacteriaceae in our province. A total of 186 carbapenem-resistant Enterobacteriaceae isolates (CRE) were collected in a grade-3 hospital in Zhejiang province. Carbapenem-resistant genes, including bla (KPC), bla (IMP), bla (VIM), bla (OXA-48) and bla (NDM-1) were screened and sequenced. Ninety isolates were identified as harboring the bla (KPC-2) genes, and five bla (NDM-1)-positive isolates were uncovered. XbaI-PFGE revealed that three bla (NDM-1)-positive K. pneumoniae isolates belonged to two different clones. S1-PFGE and southern blot suggested that the bla (NDM-1) genes were located on IncX3-type plasmids with two different sizes ranging from 33.3 to 54.7 kb (n=4) and 104.5 to 138.9 kb (n=1), respectively, all of which could easily transfer to Escherichia coli by conjugation and electrotransformation. The high-throughput sequencing of two plasmids was performed leading to the identification of a smaller 54-kb plasmid, which had high sequence similarity with a previously reported pCFNDM-CN, and a larger plasmid in which only a 7.8-kb sequence of a common gene environment around bla (NDM-1) (bla (NDM-1)-trpF- dsbC-cutA1-groEL-ΔInsE,) was detected. PCR mapping and sequencing demonstrated that four smaller bla (NDM-1) plasmids contained a common gene environment around bla (NDM-1) (IS5-bla (NDM-1)-trpF- dsbC-cutA1-groEL). We monitored the CRE epidemic in our hospital and determined that KPC-2 carbapenemase was a major risk to patient health and the IncX3-type plasmid played a vital role in the spread of the bla (NDM-1) gene among the CRE.