Antibacterial potency of biosynthesized aluminum–potassium hybrid nanoparticles using Polyalthia longifolia leaf extract against multidrug-resistant clinical isolates

Abstract

Antimicrobial resistance (AMR) poses an escalating global health threat, with projections of up to 10 million annual deaths by 2050 unless alternative therapeutic strategies are developed. Green nanotechnology offers a sustainable approach to combating multidrug-resistant (MDR) pathogens by harnessing plant-derived phytochemicals as biocompatible reducing and capping agents. This study aims to synthesize, characterize, and evaluate the antibacterial efficacy of biogenic aluminum–potassium hybrid nanoparticles (P@Al-KNPs) fabricated using aqueous leaf extract of Polyalthia longifolia against MDR clinical isolates of Staphylococcus aureus, Streptococcus sp., and Salmonella sp. P@Al-KNPs were synthesized by reacting aqueous P. longifolia leaf extract (30 mL) with a mixed AlCl3/KCl precursor solution (70 mL) at 60 °C–70 °C (pH 6.2). Physicochemical characterization employed UV–visible (Vis) spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. Antibacterial activity was assessed using the Kirby–Bauer disc diffusion method at concentrations of 50, 75, 100, and 150 µg/mL. Data were analyzed using one-way ANOVA with Duncan’s multiple range test at α = 0.05 using SPSS v.19. Successful nanoparticle formation was confirmed using a colorimetric transition and UV–Vis absorption at 408 nm (absorbance: 0.970). ATR-FTIR identified phenolic, carbonyl, and hydroxyl groups as principal mediators of biosynthesis. SEM revealed a predominantly spherical morphology (70–103 nm), and EDX confirmed Al (49.11%) and K (24.99%) as the primary constituents. Antibacterial testing demonstrated significant dose-dependent inhibition zones of 16.4 mm (S. aureus), 16.0 mm (Streptococcus sp.), and 14.3 mm (Salmonella sp.) at 150 µg/mL. The one-way ANOVA reported significant differences among concentrations (p < 0.05). In conclusion, P@Al-KNPs constitute a novel, phyto-mediated dual-metal nanoplatform with significant antibacterial activity against MDR pathogens. Their facile green synthesis and superior activity at subminimum inhibitory concentrations position them as promising candidates for biomedical antimicrobial applications.