Enhanced uptake of antibiotic resistance genes in the presence of nanoalumina

<p>Nanomaterial pollution and the spread of antibiotic resistance genes (ARGs) are global public health and environmental concerns. Whether nanomaterials could aid the transfer of ARGs released from dead bacteria into live bacteria to cause spread of ARGs is still unknown. Here, we demonstrated that nano-Al₂O₃ could significantly promote plasmid-mediated ARGs transformation into Gram-negative <i>Escherichia coli</i> strains and into Gram-positive <i>Staphylococcus aureus</i>; however, bulk Al₂O₃ did not have this effect. Under suitable conditions, 7.4 × 10⁶ transformants of <i>E. coli</i> and 2.9 × 10⁵ transformants of <i>S. aureus</i> were obtained from 100 ng of a pBR322-based plasmid when bacteria were treated with nano-Al₂O₃. Nanoparticles concentrations, plasmid concentrations, bacterial concentrations, interaction time between the nanomaterial and bacterial cells and the vortexing time affected the transformation efficiency. We also explored the mechanisms underlying this phenomenon. Using fluorescence <i>in situ</i> hybridization and scanning electron microscopy, we found that nano-Al₂O₃ damaged the cell membrane to produce pores, through which plasmid could enter bacterial cells. Results from reactive oxygen species (ROS) assays, genome-wide expression microarray profiling and quantitative real-time polymerase chain reactions suggested that intracellular ROS damaged the cell membrane, and that an SOS response promoted plasmid transformation. Our results indicated the environmental and health risk resulting from nanomaterials helping sensitive bacteria to obtain antibiotic resistance.