In Silico Characterization of bla(NDM)-Harboring Conjugative Plasmids in Acinetobacter Species

New Delhi metallo-β-lactamase (NDM)-producing clinical strains in Acinetobacter spp. have been recently reported in many countries and have received considerable attention. The vast majority of bla(NDM) cases occur on conjugative plasmids, which play a vital role in disseminating bla(NDM). To characterize the conjugative plasmids bearing bla(NDM) genes in Acinetobacter spp., we analyzed the variants of bla(NDM), conjugative transfer regions, genetic contexts of bla(NDM), and the phylogenetic pattern of the 62 predicted bla(NDM)-positive plasmids, which were selected from 1,191 plasmids of Acinetobacter species from GenBank. We identified 30 conjugative plasmids from the 62 bla(NDM)-harboring plasmids in Acinetobacter species, with the oriT sites similar to plasmid pNDM-YR7 in our study, genes coding for relaxases of the MOB(Q) family, genes encoding type IV coupling proteins (T4CPs) of the TrwB/TraD subfamily, and VirB-like type IV secretion system (T4SS) gene clusters. The genome sizes of all 30 pNDM-YR7-like plasmids ranged from 39.36 kb to 49.65 kb, with a median size of 44.56 kb. The most common species of Acinetobacter containing the bla(NDM)-positive conjugative plasmids was A. baumannii, followed by Acinetobacter lwoffii and Acinetobacter indicus. Notably, pNDM-YR7 is the first report on a bla(NDM)-positive conjugative plasmid in Acinetobacter junii. Moreover, all 30 bla(NDM)-positive conjugative plasmids in Acinetobacter species were found to contain genetic contexts with the structure ISAba14-aph(3′)-VI-ISAba125-bla(NDM)-ble. Our findings provide important insights into the phylogeny and evolution of bla(NDM)-positive plasmids of Acinetobacter species and further address their role in acquiring and spreading bla(NDM) genes in Acinetobacter species. IMPORTANCE Conjugative plasmids harboring the bla(NDM) gene play a vital role in disseminating carbapenem resistance. In this study, we first report a conjugative plasmid, pNDM-YR7, in Acinetobacter junii. Based on the genomic characteristics of the bla(NDM)-positive pNDM-YR7, we performed in silico typing and comparative analysis of bla(NDM)-positive plasmids using the 1,191 plasmids of Acinetobacter species available in the NCBI RefSeq database. We analyzed the characteristics of bla(NDM)-positive plasmids, including the variants of bla(NDM), genetic features associated with bla(NDM), conjugative transfer regions, and the phylogenetic pattern of the bla(NDM)-positive plasmids. All 30 bla(NDM)-positive conjugative plasmids were found to contain an ISAba14-aph(3′)-VI-ISAba125-bla(NDM)-ble region. This study provides novel insights into the phylogeny and evolution of bla(NDM)-harboring conjugative plasmids and contributes to the repertoire of knowledge surrounding bla(NDM)-positive plasmids in the genus Acinetobacter.