Interspecies DNA acquisition by a naturally competent Acinetobacter baumannii strain.

The human pathogen Acinetobacter baumannii possesses high genetic plasticity and frequently acquires antimicrobial resistance genes. Here we investigated the role of natural transformation in these processes. Genomic DNA from different sources, including from carbapenem-resistant Klebsiella pneumoniae strains, was mixed with A. baumannii A118 cells. Selected transformants were analysed by whole-genome sequencing. In addition, bioinformatics analyses and in silico gene flow prediction were also performed to support the experimental results. Transformant strains included some that became resistant to carbapenems or changed their antimicrobial susceptibility profile. Foreign DNA acquisition was confirmed by whole-genome analysis. The acquired DNA most frequently identified corresponded to mobile genetic elements, antimicrobial resistance genes and operons involved in metabolism. Bioinformatics analyses and in silico gene flow prediction showed continued exchange of genetic material between A. baumannii and K. pneumoniae when they share the same habitat. Natural transformation plays an important role in the plasticity of A. baumannii and concomitantly in the emergence of multidrug-resistant strains.