Identification and characterization of a novel incompatibility group X3 plasmid carrying bla NDM-1 in Enterobacteriaceae isolates with epidemiological links to multiple geographical areas in China

The New Delhi metallo-β-lactamase (NDM-1) is one of the most important resistance traits in Enterobacteriaceae. We characterized nine bla NDM-1 producing Enterobacteriaceae recovered from seven patients who have recently travelled or been treated in India (n=1) or mainland China (n=6) during December 2010-May 2012. All the China-linked patients had no links to the Indian subcontinent. The bla NDM-1 carrying plasmids belonged to the novel IncX3 (∼50 kb, in seven isolates including two Escherichia coli, two Klebsiella pneumoniae, one Citrobacter freundii, one Enterobacter aerogenes and one E. cloacae), IncA/C2 (∼140 kb, in one E. coli) or FII-F1B groups (∼110 kb, in one E. coli). Restriction fragment length polymorphism analysis of the seven IncX3 plasmids revealed identical pattern in six and two bands difference in the remaining one. The IncX3 plasmids carrying bla NDM-1 were epidemiologically linked to Guangzhou (n=1), Hunan (n=4), Haifeng (n=1) and Dongguan (n=1) in mainland China. Complete sequencing of the IncX3 plasmid pNDM-HN380 revealed that it was 54 035 bp long and encoded 52 open reading frames. The bla NDM-1 gene was found in a transposon-like structure flanked by ISAba125 and IS26, inserted into the plasmid genetic load region. The sequences of the bla NDM-1 containing module within the two IS elements were identical to those previously described for bla NDM-1-positive Tn125 in the plasmids or chromosome of Acinetobacter isolates. In summary, this is the first description of IncX3 plasmids carrying bla NDM-1. The findings indicate the worrisome involvement of an epidemic plasmid in the dissemination of NDM-1 in China.