Molecular characterization of blaNDM-1 in an Acinetobacter baumannii strain isolated in Germany in 2007

Objectives: To investigate the genetic environment of the metallo-beta-lactamase gene bla(NDM-1) in an Acinetobacter baumannii isolated in 2007 in a German hospital. Methods: Antimicrobial susceptibility testing was performed and resistance genes were characterized by PCR amplification and sequencing. Transferability of beta-lactam resistance was tested by broth mating assays and transformation of plasmids. The genetic background of bla(NDM-1) was analysed by primer walking. Typing of the A. baumannii strain was performed by repetitive extragenic palindromic sequence-based PCR (rep-PCR) using the DiversiLab system. Results: The multidrug-resistant A. baumannii isolate harboured beta-lactamase genes bla(NDM-1) and intrinsic bla(OXA-64), but without the insertion sequence ISAba1 often located upstream. Transfer of carbapenem resistance by conjugation and transformation failed. Hybridization of isolated plasmid DNA with bla(NDM) probes was not successful. Shotgun cloning of whole genomic DNA and sequence analyses revealed that bla(NDM-1) was located between two insertion elements of ISAba125. Furthermore, this bla(NDM-1)-containing transposon structure was integrated into a chromosomal gene encoding a putative A. baumannii major facilitator superfamily (MFS) metabolite/H+ symporter. Conclusions: The metallo-beta-lactamase gene bla(NDM-1) in this A. baumannii strain was integrated in the chromosome on a new transposon structure composed of two copies of insertion sequence ISAba125. The variability of the genetic environment of bla(NDM-1) likely facilitates the rapid dissemination of this gene within many Gram-negative bacterial species.