Antibiotic-resistant bacteria represent a global risk to public health. Horizontal gene transfer, a common mechanism for genetic exchange in bacteria, plays an essential role in the acquisition of resistance genes. In this work, we evaluated the effect of sub-lethal concentrations of antibiotics on plasmid transfer by conjugation and transformation in the opportunistic pathogen Klebsiella pneumoniae. Despite not being naturally competent, this bacterium could acquire extracellular DNA from

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... lular DNA from various plasmids at a very low frequency, which increased upon incubating cells with the aminoglycoside antibiotics amikacin and gentamicin. Transfer by conjugation analyzed using a clinical isolate carrying plasmid pNDM-1 also increased in the presence of sub-lethal concentrations of antibiotics. An RNAseq analysis showed differential expression of several genes when cells were incubated in the presence of sub-lethal concentrations of amikacin suggesting metabolic and regulatory changes, as well as alteration of cell envelope components that could affect the uptake of foreign DNA. These results suggest that sub-lethal concentrations of some aminoglycosides, in particular amikacin, can promote the transfer of resistance-bearing genetic elements in K. pneumoniae, which is relevant for understanding the spread of resistance determinants in this human pathogen.