Metal nanoparticles as next-generation therapeutics against antimicrobial resistance: mechanisms, functionalization, and translational potential.

Antimicrobial resistance (AMR) poses a major global health threat, driven by bacterial defense mechanisms such as efflux pumps, enzyme-mediated drug inactivation, target site modification, and biofilm formation. Metal nanoparticles (NPs), including silver, gold, iron oxide, and zinc oxide, offer a potential multi-target strategy to dismantle these resistance pathways. Their antimicrobial activity stems from direct membrane disruption, induction of oxidative stress, and, crucially, the modulation of bacterial gene expression, including downregulation of efflux pump and biofilm-related genes and disruption of quorum-sensing networks. The efficacy and specificity of NPs are significantly enhanced through advanced functionalization strategies, such as organic ligand conjugation, antibody coupling, and green synthesis approaches using biological resources, enabling targeted drug delivery and reduced off-target toxicity. Despite promising translational applications in antimicrobial coatings, wound dressings, and adjuvant therapies, clinical adoption faces hurdles including potential cytotoxicity, unpredictable pharmacokinetics, and the need for standardized manufacturing. Future directions involve the development of environmentally responsive "smart" NPs, nanoparticle-mediated delivery of siRNA to suppress resistance genes, and the integration of multi-omics approaches to decipher NP-bacteria interactions at the molecular level. Collectively, engineered metal NPs represent a promising platform for next-generation antimicrobial strategies and may help address multidrug resistance through simultaneous molecular and physical effects.