Functionalization and Antimicrobial Evaluation of Azadirachta indica Leaf-Synthesized Silver Nanoparticles with Amoxicillin

Abstract The rapid emergence of antimicrobial resistance, particularly among multidrug-resistant (MDR) and extended-spectrum β-lactamase (ESBL)-producing Escherichia coli, necessitates the development of novel therapeutic strategies. In this study, we report the green synthesis and functionalization of silver nanoparticles (AgNPs) using Azadirachta indica leaf extract conjugated with amoxicillin (Amoxicillin-AI-AgNPs) to enhance antibacterial efficacy. The synthesized nanoparticles were characterized using UV–Vis spectroscopy, FTIR, XRD, DLS, SEM, EDAX, and TEM analyses, confirming the formation of stable, spherical, crystalline nanoparticles with an average size of ∼87 nm and a zeta potential of −28.73 mV. High conjugation efficiency (∼94%) of amoxicillin with AgNPs was achieved after 96 hours of incubation. Antimicrobial activity assessed against 88 clinical MDR and ESBL-producing E. coli isolates demonstrated significantly enhanced efficacy of Amoxicillin-AI-AgNPs compared to amoxicillin alone, with minimum inhibitory concentrations (MIC) ranging from 1.56 to 6.25 µg/mL and minimum bactericidal concentrations (MBC) between 25–100 µg/mL. Cytotoxicity evaluation on HEK-293 cells revealed a relatively high IC50 value (382.14 ± 6.59 µg/mL), indicating low toxicity at antibacterial doses. The synergistic interaction between AgNPs and amoxicillin likely contributes to improved bacterial inhibition and overcoming resistance mechanisms. Overall, this study highlights the potential of plant-mediated antibiotic– nanoparticle conjugates as an effective and biocompatible approach to combat antibiotic-resistant bacterial infections. Competing Interest Statement The authors have declared no competing interest.