NDM-producing Enterobacteriaceae in a Chinese hospital, 2014-2015: identification of NDM-producing Citrobacter werkmanii and acquisition of blaNDM-1-carrying plasmid in vivo in a clinical Escherichia coli isolate

New Delhi metallo-beta-lactamase (NDM)-producing Enterobacteriaceae (NPE) shows prevalence in China. Little is known about the mechanisms related to the spread of NPE. Recently, a total of 51 non-duplicated NPE isolates were collected from a tertiary-care hospital in China and analysed for genetic relatedness by PFGE, antimicrobial susceptibility by Etest and sequence type by multilocus sequence typing. S1-PFGE and Southern blot analysis or PCR amplification were used for plasmid profiling. Between 2014 and 2015, 22 Escherichia coli, 10 Klebsiella pneumoniae, 9 Enterobacter cloacae, 2 Enterobacter aerogenes, 3 Providencia rettgeri, 1 Klebsiella oxytoca, 1 Proteus mirabilis, 1 Citrobacter freundii, 1 Citrobacter werkmanii and 1 Raoultella planticola were identified as NPE. Results of PFGE and multilocus sequence typing showed that most strains were genetically unrelated. Among the 45 bla(NDM)-carrying plasmids, there were 25 IncX3 plasmids with a size of about 30 to 50 kb, one 100 kb IncX3 plasmid, 11 IncA/C plasmids with a size range from 70 to 300 kb, six 90 to 120 kb IncB/O plasmids, one IncN plasmid with a size of 100 kb and one 140 kb IncFrep plasmid. An NDM-1-producing isolate of C. werkmanii was identified, which had not been reported previously. An Escherichia coli strain was found acquiring a bla(NDM-1)-carrying IncFrep plasmid in vivo during infection. In conclusion, an NDM-1-producing isolate of C. werkmanii was identified. An Escherichia coli strain acquired a bla(NDM-1)-carrying plasmid in vivo. IncX3 and IncA/C plasmids with various sizes might have emerged as the main platforms mediating the spread of the bla(NDM) genes in China.