Interbacterial transfer of carbapenem resistance and large antibiotic resistance islands by natural transformation in pathogenic Acinetobacter

Extensive genetic exchanges through horizontal gene transfers (HGT) are one of the driving forces behind the spread of antibiotic resistance among Acinetobacter isolates. In this work, we aimed to evaluate the contribution of natural transformation, a mechanism of HGT commonly found in A. baumannii clinical isolates, in the spread of the carbapenems resistance. An effective and rapid transfer of the carbapenems resistance genetic determinants was possible between different Acinetobacter spp. in experimental conditions that mimic a bacterial community. Furthermore, the naturally transformable A. nosocomialis strain M2 was able to acquire the carbapenems resistance in only a few hours at a high frequency, through natural transformation of a high-quality DNA released by a donor strain. Genetic analyses of transformants showed that natural transformation fostered the acquisition of large DNA fragment containing mobile genetic elements such as the Tn2006 or even a large resistance island named AbaR4 that carry the blaOXA-23 gene conferring the resistance to carbapenems.