# Enterococcus hirae‐Mediated ZnO and CuO/ZnO Nanoparticles: Synergistic Antimicrobial Combinations Against MDR Pathogens

## TL;DR

This study uses Enterococcus hirae to create nanoparticles that show strong antimicrobial and antioxidant properties, especially when combined with antibiotics to fight drug-resistant bacteria.

## Contribution

The first use of Enterococcus hirae for extracellular synthesis of CuO/ZnO nanoparticles with demonstrated synergistic antimicrobial effects.

## Key findings

- CuO/ZnO nanoparticles showed 62.5% greater antimicrobial efficacy than ZnO alone.
- Synergistic interactions between nanoparticles and antibiotics were observed against Klebsiella pneumoniae.
- E-CuO/ZnO nanoparticles exhibited superior antioxidant activity with an IC50 of 5.528 μg/mL.

## Abstract

The rapid emergence of multidrug‐resistant (MDR) pathogens, particularly in hospital wastewater, poses a serious threat to public health and emphasizes the need for alternative antimicrobial strategies. In this study, Enterococcus hirae, an environmentally derived strain, was used for the first time in the extracellular green synthesis of zinc oxide nanoparticles (ZnO NPs) and copper oxide/zinc oxide nanoparticles (CuO/ZnO NPs). The nanoparticles were characterized using standard techniques. Ultraviolet–visible (UV‐Vis) spectra, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and energy‐dispersive X‐ray spectroscopy (EDS) confirmed both nanoparticle formation, size, and morphology. Antimicrobial activity against Staphylococcus aureus (ATCC 6538), Morganella morganii, Kerstersia gyiorum, and Klebsiella pneumoniae was evaluated using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays, showing a 62.5% greater efficacy of bimetallic NPs than ZnO alone. The 2,2‐diphenyl‐1‐picrylhydrazyl hydrate (DPPH) assay revealed that E‐CuO/ZnO NPs exhibited superior antioxidant activity with the lowest IC50 of 5.528 μg/mL, outperforming E‐ZnO NPs, which is attributed to the synergistic effect between ZnO and CuO NPs. The combination of E‐ZnO and E‐CuO/ZnO nanoparticles with ciprofloxacin (CIP) and ceftazidime (CAZ) was evaluated against MDR isolates. Synergistic interactions were observed particularly against K. pneumoniae. This study confirms effective E. hirae‐mediated synthesis and the enhanced antibacterial and antioxidant potential of CuO/ZnO NPs, supporting eco‐friendly strategies against MDR infections, with synergistic interactions observed with conventional antibiotics, particularly against K. pneumoniae, indicating that the nanoparticles can enhance antibiotic efficacy.