Novel Plasmid and Its Variant Harboring both a blaNDM-l Gene and Type IV Secretion System in Clinical Isolates of Acinetobacter lwoffii

The spread of the bla(NDM-1) gene is gaining worldwide attentions. This gene is usually carried by large plasmids and has been discovered in diverse bacteria since it was originally found in Klebsiella pneumoniae. Here we report the complete sequences of a bla(NDM-1)-bearing plasmid, pNDM-BJ01, and its variant, pNDM-BJ02, isolated from clinical Acinetobacter lwoffii strains. The plasmid pNDM-BJ01 is 47.3 kb in size and cannot be classified into any known plasmid incompatibility group, thus representing a novel plasmid with an unknown maintenance mechanism. This plasmid contains both a bla(NDM-1) gene and a type IV secretion system (T4SS) gene cluster. The T4SS is assigned to the P-type T4SS group, which usually encode a short, rigid pilus, and the bla(NDM-1) gene is located within a composite transposon flanked by two insertion elements of ISAba125. Plasmid pNDM-BJ02 is nearly identical to pNDM-BJ01 except that one copy of the ISAba125 element is missing, and it is therefore regarded as a variant of pNDM-BJ01. Sequence alignment indicated that this bla(NDM-1)-containing composite transposon, which can also be captured by other mobile elements, was probably a product of multiple recombination events and can move as a whole by transposition.