Characterization of Plasmids in Extensively Drug-Resistant Acinetobacter Strains Isolated in India and Pakistan

Abstract

ABSTRACTTheblaNDM-1gene is associated with extensive drug resistance in Gram-negative bacteria. This probably spread toEnterobacteriaceaefromAcinetobacterspp., and we characterized plasmids associated withblaNDM-1inAcinetobacterspp. to gain insight into their role in this dissemination. Four clinical NDM-1-producingAcinetobacterspecies strains from India and Pakistan were investigated. A plasmid harboringblaNDM-1, pNDM-40-1, was characterized by whole-genome sequencing ofAcinetobacter bereziniaeCHI-40-1 and comparison with related plasmids. The presence of similar plasmids in strains from Pakistan was sought by PCR and sequencing of amplicons. Conjugation frequency was tested and stability of pNDM-40-1 investigated by real-time PCR of isolates passaged with and without antimicrobial selection pressure.A. bereziniaeandAcinetobacter haemolyticusstrains contained plasmids similar to the pNDM-BJ01-like plasmids identified inAcinetobacterspp. in China. The backbone of pNDM-40-1 was almost identical to that of pNDM-BJ01-like plasmids, but the transposon harboringblaNDM-1, Tn125, contained two short deletions.Escherichia coliandAcinetobacterpittiitransconjugants were readily obtained. Transconjugants retained pNDM-40-1 after a 14-day passage experiment, although stability was greater with meropenem selection. Fragments of pNDM-BJ01-like plasmid backbones are found nearblaNDM-1in some genetic contexts fromEnterobacteriaceae, suggesting that cross-genus transfer has occurred. pNDM-BJ01-like plasmids have been described in isolates originating from a wide geographical region in southern Asia.In vitrodata on plasmid transfer and stability suggest that these plasmids could have contributed to the spread ofblaNDM-1intoEnterobacteriaceae.