Biogenic synthesis of silver nanoparticles using combined leaf extracts of Azadirachta indica and Ocimum sanctum: physicochemical characterization and antibacterial efficacy against drug-resistant pathogens including MRSA

Silver nanoparticles (AgNPs) synthesized by green routes represent a compelling solution to the global antimicrobial resistance (AMR) crisis. Here we report the first preparation of AgNPs using a binary 1:1 aqueous leaf extract combination of Azadirachta indica (Neem) and Ocimum sanctum (Tulsi), designated NL-AgNPs, exploiting the complementary phytochemical repertoires of both plants. Synthesis was optimized over a multi-parametric matrix (AgNO3 concentration, temperature, pH, time) yielding NL-AgNPs confirmed by a surface plasmon resonance peak at 421 nm. Field emission scanning electron microscopy (FESEM) established a mean diameter of 22.8 ± 3.2 nm; X-ray diffraction (XRD) confirmed face-centred cubic (FCC) metallic silver; and dynamic light scattering (DLS) yielded a zeta potential of − 31.7 ± 2.9 mV. FTIR spectroscopy identified eugenol, rosmarinic acid, quercetin, and gallic acid as primary reducing and capping agents. Antibacterial evaluation against six ATCC-certified strains including methicillin-resistant Staphylococcus aureus (MRSA ATCC 33591) demonstrated zones of inhibition of 15.8–22.6 mm and minimum inhibitory concentrations (MICs) of 3.12–25.0 µg/mL. NL-AgNPs showed activity against ampicillin-resistant MRSA (zone = 18.9 mm; MIC = 6.25 µg/mL), outperforming either individual plant extract and approaching fluoroquinolone efficacy. This hazardous-chemical-free, scalable approach offers a viable green route to clinically relevant antimicrobial nanomaterials.