Detection of an Escherichia coli Sequence Type 167 Strain with Two Tandem Copies ofblaNDM-1in the Chromosome
ABSTRACTNew Delhi metallo-β-lactamase-1 (NDM-1)-producingEnterobacteriaceaehas disseminated rapidly throughout the world and poses an urgent threat to public health. Previous studies confirmed that theblaNDM-1gene is typically carried in plasmids but rarely in chromosome. We discovered a multidrug-resistantEscherichia colistrain Y5, originating from a urine sample and containing theblaNDM-1gene, which did not transfer by either conjugation or electrotransformation. We confirmed the possibility of its chromosome location by S1-pulsed-field gel electrophoresis (PFGE) and XbaI-PFGE, followed by Southern blotting. To determine the genomic background ofblaNDM-1, the genome of Y5 was completely sequenced and compared to other reference genomes. The results of our study revealed that this isolate consists of a 4.8-Mbp chromosome and three plasmids, it is an epidemic clone of sequence type (ST) 167, and it shows 99% identity withEscherichia coli6409 (GenBank accession no.CP010371), which lacks the sameblaNDM-1gene-surrounding structure as Y5. TheblaNDM-1gene is embedded in the chromosome along with two tandem copies of an insertion sequence common region 1 (ISCR1) element (sul1-ARR-3-cat-blaNDM-1-bleo-ISCR1), which appears intact in the plasmid fromProteus mirabilis(GenBank accession no.KP662515). The genomic context indicates that the ISCR1element mediated theblaNDM-1transposition from a single source plasmid to the chromosome. Our study is the first report of anEnterobacteriaceaestrain harboring a chromosomally integratedblaNDM-1, which directly reveals the vertical spreading pattern of the gene. Close surveillance is urgently needed to monitor the emergence and potential spread of ST167 strains that harborblaNDM-1.