Interspecies DNA acquisition by a naturally competentAcinetobacter baumanniistrain

Abstract

ABSTRACTAcinetobacter baumanniiis a human pathogen that frequently acquires antibiotic resistance genes leading to the emergence of multi-drug-resistant (MDR) strains. To investigate the role of transformation in the acquisition of resistance determinants by this species, the susceptible strain A118 was exposed to genomic DNA of carbapenem-resistantKlebsiella pneumoniae(CRKp). Resistant transformants were obtained and an increase in the resistance level to all β-lactam antibiotics was observed. Whole genome analysis of transformant clones demonstrated the acquisition of CRKp DNA. The most frequently acquired genes correspond to mobile elements, antibiotic resistance genes, and operons involved in metabolism. Bioinformatic analyses andin silicogene flow prediction strengthen our findings, showing that a continuing exchange of genetic material betweenA. baumanniiandK. pneumoniaeoccurs when they share the same niche. Our results reinforce the idea that natural transformation may play a key role in the increasing emergence ofA. baumanniiMDR.IMPORTANCESince the characterization of antibiotic resistance in the late ‘50s, antibiotic resistance propagation was classically associated with horizontal gene transfer (HGT) mediated by plasmids bearing multiple resistance genes. Here we show that, at least in the human pathogenA. baumannii, transformation also plays a major role in the acquisition of antibiotic resistance determinants. This study unravels that at least for certain pathogens the propagation of resistance genes occurs by alternative HGT mechanisms which in the past have been unappreciated.