Phytochemical-capped copper oxide nanoparticles from Curcuma longa and Tridax procumbens: Selective activity against multidrug-resistant clinical isolates

Antimicrobial resistance (AMR) presents a critical global health challenge necessitating novel therapeutic strategies. This study reports the green synthesis of copper oxide nanoparticles (CuO NPs) utilizing phytochemical extracts from Curcuma longa and Tridax procumbens as bifunctional reducing and capping agents. The synthesized nanoparticles, designated Curamine-B and Tridax-A, were comprehensively characterized using UV–Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Phytochemical profiling by high-performance liquid chromatography and electrospray ionization mass spectrometry identified curcuminoids, flavonoids, phenolic acids, and terpenoids as key bioactive constituents. XRD analysis revealed mixed-phase nanocomposites: Curamine-B comprised a curcuminoid matrix with Cu₂O and CuO phases (crystallite sizes 6–80 nm), while Tridax-A exhibited a polyphasic Cu⁰/Cu⁺/Cu²⁺ system (10–50 nm). Antimicrobial efficacy was evaluated against eight multidrug-resistant clinical isolates using the agar well diffusion method. Curamine-B demonstrated selective activity toward Gram-positive bacteria, with maximum inhibition zones of 18.5 mm for Staphylococcus epidermidis, whereas Tridax-A exhibited broader-spectrum activity including Gram-negative pathogens, achieving maximum inhibition of 24.0 mm for Pseudomonas plecoglossicida. Both formulations exhibited comparable antimicrobial potency (Mann–Whitney U test, p = 0.7486), establishing phytochemical composition as the primary determinant of selective activity and enabling rational design strategies for engineering pathogen-targeted copper nanocomposites independent of copper oxidation state. These findings establish plant-mediated synthesis as a tunable, cost-effective, and environmentally sustainable approach for developing next-generation antimicrobial nanomaterials capable of combating multidrug-resistant pathogens.