Evolutionary strategies in response to the transmission risk of antimicrobial resistance upon repeated exposure to nanoparticles.

Nanoparticles (NPs) contribute to antimicrobial resistance transmission through bacterial transformation. However, transformation risk under repeated exposure to NPs remains largely unexplored. Here, two representative engineered NPs frequently detected in the environment, i.e., metal-based CuO and polymer-based polystyrene (PS) NPs, were selected as model NPs. Comparative evolution experiments were conducted to investigate the transformation of Escherichia coli by plasmid-borne antibiotic resistance genes upon repeated exposure to NPs. Bacterial growth assays and pili or curli adhesion dynamics simulation were conducted to assess NPs cytotoxicity and aggregation characteristics. Transcriptomics revealed that transformation risk was closely associated with NPs-modulated bacterial defense strategies, including antioxidant defense, cell wall-fortification, DNA and protein damage repair, and energy supply. Notably, repeated exposure to CuO NPs triggered severe oxidative stress of bacterial population due to their high-cytotoxicity and low-aggregation, thereby impairing bacterial defense system and evolving progressively severe antimicrobial resistance. Contrastingly, repeated exposure to PS NPs with low-cytotoxicity and high-aggregation via van der Waals attraction, generated milder oxidative stress. This incrementally enhanced bacterial defense effectiveness, potentially reversing antimicrobial resistance to restore bacterial sensitivity. These findings elucidated the importance of NPs-modulated defense effectiveness in bacterial transformation, providing valuable insights for NPs design or application and antimicrobial resistance risk assessment.