Biophysical characterization and antibacterial activity of green-synthesized silver nanoparticles from pomegranate (Punica granatum) peel extract against multidrug-resistant clinical isolates

Abstract

For several common infections, the spread of multidrug-resistant (MDR) bacteria has narrowed the range of usable antibiotics. Silver nanoparticles (AgNPs) are one candidate replacement, and making them with plant extracts keeps both the cost and the use of toxic reagents low. We set out to make AgNPs with pomegranate peel extract, describe their properties, and see how well they act on MDR isolates from patients and how toxic they are to Vero cells. An aqueous peel extract, with no other reducing agent, was added to 1 mM silver nitrate. The resulting particles were characterized using UV–visible and FTIR spectroscopy, X-ray diffraction, transmission electron microscopy, dynamic light scattering and zeta-potential measurement. Five patient isolates were tested by agar well diffusion, broth microdilution (MIC/MBC) and time-kill experiments; Vero cell toxicity was measured by MTT. SPR peak at 425 nm, almost unchanged after 30 days at 4 °C. FTIR band shifts (phenolic O–H, C=O) implicated extract polyphenols in reduction and capping. TEM: spherical particles, 22.5 ± 6.1 nm; DLS: 38.6 nm, PDI 0.21; zeta potential −28.4 mV. The lowest MIC (8 µg/mL) was recorded for Escherichia coli and the highest (32 µg/mL) for both methicillin-resistant Staphylococcus aureus (MRSA) and Klebsiella pneumoniae. At 2× MIC, viable counts dropped by 3 log₁₀ within 8 h (E. coli) and 12 h (MRSA). The Vero IC₅₀ was 112.4 µg/mL (selectivity index 3.5–14.1). The peel-derived AgNPs were bactericidal against MDR isolates at concentrations under the Vero IC₅₀. Topical rather than systemic use looks like the most realistic application.