Enantioselective interactions of silver nanoparticles and chiral antibiotics in driving resistance evolution in activated sludge

The stereochemistry of antibiotics significantly affects resistance development. With rising antibiotic resistance, nanotechnology is emerging as a promising solution, potentially increasing the likelihood of nanoparticle coexistence with antibiotics in wastewater treatment plants (WWTPs). However, the influence of nanoparticles on chiral antibiotics induced resistance remains unclear. This study employed chemical characterization, metagenomics, and molecular docking to comprehensively elucidate the resistance mechanisms induced by the combination of silver nanoparticles (AgNPs) and chiral antibiotics (ofloxacin: OFL and levofloxacin: LEV). AgNPs significantly altered the abundance and composition of antibiotic and metal resistance genes, as well as the conjugative transfer of the RP4 plasmid among activated sludge communities, with the OFL_AgNPs combination exhibiting a higher resistance potential than LEV_AgNPs. Mechanistic studies revealed that chiral antibiotics selectively interact with AgNPs, promoting Ag + release, enhancing antibiotic uptake, and forming stable complexes. These interactions reshaped microbial functions, including cell membrane permeability, oxidative stress response, quorum sensing, and extracellular secretion, thereby shaping resistance profiles. This study reveals previously overlooked enantiomer-specific risks associated with nanoparticle-antibiotic interactions and provides a foundation for strategies to mitigate ARG dissemination in wastewater treatment and broader environmental systems.