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

<div><p>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 <i>bla</i>_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 <i>bla</i>_KPC, <i>bla</i>_IMP, <i>bla</i>_VIM, <i>bla</i>_OXA-48 and <i>bla</i>_NDM-1 were screened and sequenced. Ninety isolates were identified as harboring the <i>bla</i>_KPC-2 genes, and five <i>bla</i>_NDM-1-positive isolates were uncovered. XbaI-PFGE revealed that three <i>bla</i>_NDM-1-positive <i>K</i>. <i>pneumoniae</i> isolates belonged to two different clones. S1-PFGE and southern blot suggested that the <i>bla</i>_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 <i>Escherichia coli</i> 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 <i>bla</i>_NDM-1 (<i>bla</i>_NDM-1-<i>trpF</i>- <i>dsbC</i>-<i>cutA1</i>-<i>groEL</i>-Δ<i>InsE</i>,) was detected. PCR mapping and sequencing demonstrated that four smaller <i>bla</i>_NDM-1 plasmids contained a common gene environment around <i>bla</i>_NDM-1 (IS<i>5</i>-<i>bla</i>_NDM-1-<i>trpF</i>- <i>dsbC</i>-<i>cutA1</i>-<i>groEL</i>). 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 <i>bla</i>_NDM-1 gene among the CRE.</p>