Complete sequencing of the bla _NDM-1-positive IncA/C plasmid from Escherichia coli ST38 isolate suggests a possible origin from plant pathogens

The complete sequence of the plasmid pNDM-1_Dok01 carrying New Delhi metallo-β-lactamase (NDM-1) was determined by whole genome shotgun sequencing using Escherichia coli strain NDM-1_Dok01 (multilocus sequence typing type: ST38) and the transconjugant E. coli DH10B. The plasmid is an IncA/C incompatibility type composed of 225 predicted coding sequences in 195.5 kb and partially shares a sequence with bla _CMY-2-positive IncA/C plasmids such as E. coli AR060302 pAR060302 (166.5 kb) and Salmonella enterica serovar Newport pSN254 (176.4 kb). The bla _NDM-1 gene in pNDM-1_Dok01 is terminally flanked by two IS903 elements that are distinct from those of the other characterized NDM-1 plasmids, suggesting that the bla _NDM-1 gene has been broadly transposed, together with various mobile elements, as a cassette gene. The chaperonin groES and groEL genes were identified in the bla _NDM-1-related composite transposon, and phylogenetic analysis and guanine-cytosine content (GC) percentage showed similarities to the homologs of plant pathogens such as Pseudoxanthomonas and Xanthomonas spp., implying that plant pathogens are the potential source of the bla _NDM-1 gene. The complete sequence of pNDM-1_Dok01 suggests that the bla _NDM-1 gene was acquired by a novel composite transposon on an extensively disseminated IncA/C plasmid and transferred to the E. coli ST38 isolate.