Through quorum sensing, Pseudomonas aeruginosa resists noble metal-based nanomaterials toxicity

Noble metal-based nanomaterials (NMNs), such as platinum nanoparticles (Pt@NPs) and palladium nanoparticles (Pd@NPs), are increasingly being used as antibacterial agents. However, little information is available on bacterial resistance to NMNs. In this study, owing to their oxidase-like and peroxidase-like properties, both Pt@NPs and Pd@NPs induce reactive oxygen species (ROS) and manifest antibacterial activities: 6.25 mu g/mL of either Pt@NPs or Pd@NPs killed >50% of Staphylococcus aureus strain ATCC29213. However, Pseudomonas aeruginosa strain PAO1 completely resisted 12.5 mu g/mL of Pt@NPs and 6.25 mu g/mL of Pd@NPs. Compared to the non-NMN groups, these NMNs promoted 2-3-fold upregulation of the quorum sensing (QS) gene lasR in strain PAO1. In fact, the lasR gene upregulation induced a 1.5-fold reduction in ROS production and increased biofllm formation by 11% (Pt@NPs) and 27% (Pd@NPs) in strain PAO1. The Delta lasR mutants (lasR gene knock out in strain PAO1), became sensitive to NMNs. The survival rates of Delta lasR mutants at 12.5 mu g/mL Pt@NPs and Pd@NPs treatments were only 77% and 58%, respectively. This is the first report indicating that bacteria can resist NMNs through QS. Based on these results, evaluation of the ecological risks of using NMNs as antibacterial agents is necessary. (C) 2020 Elsevier Ltd. All rights reserved.