Antibacterial Activity of Green-Synthesized Zinc Oxide Nanoparticles Against Multidrug-Resistant Clinical Pathogens

INTRODUCTION
Bacterial diseases provide a significant concern for human health, having been the second leading cause of death as of 2019 [1]. In recent years, a primary worry associated with microbial illnesses is drug resistance. The World Health Organization asserted that, consequently, infections have become more challenging to treat [2]. Since the advent of antibiotics in the 20th century, bacteria have developed by acquiring defensive mechanisms that diminish or eliminate antibiotic efficacy [3,4]. Currently, pharmaceutical corporations are diminishing their interest in the study of novel antibiotics due to elevated expenses and the protracted period of studies, coupled with uncertain financial and therapeutic outcomes [5]. To solve antibiotic resistance, the WHO established a list of priority infections necessitating the development of novel antimicrobials [6]. It encompasses ‘ESKAPE’ pathogens, including Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. The majority are multidrug-resistant isolates, presenting a significant difficulty in clinical practice. It markedly prolongs hospital duration, elevates care expenses, and heightens fatality rates. Furthermore, ESKAPE pathogens are the predominant cause of nosocomial infections globally [7].
Drug resistance results from several complex mechanisms, including increased efflux pump expression, which removes medications from the bacterial cell; genes that change the binding substrate, which changes drug targets; and proteins and enzymes that alter pharmaceuticals [8]. Multidrug-resistant organisms include E. coli, S. aureus, and P. aeruginosa [9]. Bacteria build biofilms to resist antibiotics [10]. A “structured community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface” is a bacterium biofilm, which helps bacteria survive in hostile settings [11]. They exchange nutrients via channels and express various genes in various regions of biofilm [12]. Biofilm spatial heterogeneity permits some of the biofilm to withstand antibiotic attack, thereby causing antibacterial resistance [11,13,14]. Antimicrobials diffuse slower in biofilms than in water [11,15], allowing bacteria biofilms to tolerate antibiotic concentrations up to 1000 times higher than planktonic bacteria [16]. Therefore, it is imperative to explore novel therapeutic strategies for the treatment of infections induced by ESKAPE pathogens. Currently, multidrug resistance (MDR) constitutes the primary obstacle in the development of antibacterial drugs, posing a significant risk to human health and presenting a substantial concern for healthcare system expenditures [15]. Accordingly, there is an immediate necessity to identify alternative approaches that can effectively address bacterial infections, with nanomaterials being potential options for antibacterial efficacy [17].
Nanotechnology encompasses the creation and manipulation of nano-scale information inside a restricted area of materials, devices, and measurements. Materials at the nanoscale are engineered into discrete units termed nanoparticles (NPs), which consist of atoms and molecules measuring between 1 and 100 nm in size. It is widely utilised to create more efficient approaches in technology, energy conservation, scientific research, medicine, and various other domains. Nanoscale particles are produced using several methodologies, encompassing biological, chemical, and physical techniques. These methods are categorised as bottom-up and top-down approaches [18]. Biological or green synthesis is a bottom-up process that uses natural and ecologically acceptable reducing agents. Sometimes green materials are utilised as end-capping agents and dispersants [19]. Green nanoparticle synthesis is simple to solve cost-effective, and eco-friendly. However, green synthesis strategies for nanoparticles may improve their properties due to their smaller dimensions, particular form, and unique biological substrates [20].
Zinc oxide nanoparticles (ZnO-NPs) are metal oxide nanomaterials with unique physical and chemical characteristics. These inorganic chemicals have many everyday uses. ZnO-NPs are the most widely used metal oxide nanoparticles because their optical and chemical properties can be easily adjusted by changing their morphology, wide bandgap, and high excitation binding energy, making them potent photocatalytic and photo-oxidizing moiety against biological and chemical species [21]. They demonstrate less toxicity to the human body and ensure biocompatibility, as the Zn ion (Zn+2), a soluble variant of ZnO, is a trace element found in the human physiological system. ZnO has exhibited biodegradable in both its bulk form and as nanoparticle [22]. One of the most therapeutic plants is pomegranate (Punica granatum L.). In the Punicaceae family, its common name comes from the Latin words ponus and granatus, meaning “seeded apple.” This wonderful fruit, from Afghanistan, Iran, China, and India, is eaten globally [23]. Fruit structure demonstrates its medicinal properties. The internal membrane network of pomegranate peels (PoP) accounts for 26–30% of the fruit weight. Phenolic chemicals such anthocyanins, catechins, and hydrolysable tannins like punicalin, pedunculagin, punicalagins, gallic, and ellagic acid are abundant in these peels. Their concentration in the peel and juice accounts for 92% of the fruit’s antioxidant action, according to research [24]. Also, Gallic acid, ellagic acid, and punicalagin are powerful antibacterials and free radical scavengers.
They are particularly effective against enteric infections such E. coli, Salmonella, Shigella, and Vibrio cholerae [25]. Pomegranate peel extract (PoPx) has been used therapeutically for ages in many cultures. Egyptians used it to cure inflammation, diarrhoea, intestinal parasites and respiratory difficulties. 
This old wisdom has prompted rigorous modern scientific studies into human health. The active compounds in pomegranate extracts prevent and treat gastro mucosal injuries, cancer chemoprevention and diabetes related oxidative damage according to recent studies [26]. The antibacterial effect of PoP phenolics is based on mechanistic evidence that shows how lysis of microbial cells occurs through the precipitation of membrane proteins. Without further enrichment from other fruit sections, the peel’s high phytochemical concentration makes it a useful traditional and scientific asset [27]. When used in nanoparticle manufacturing, the bioactive components of pomegranate peels help stabilise and reduce the size of the final product. 
The resulting ZnO-NPs can have improved optical characteristics, size, and shape when these chemicals are added. Metallic nanoparticles have gained recognition for their substantial antibacterial efficiency against human illnesses [28], and nanotechnology offers good solutions across a variety of applications. Therefore, ZnO-NPs’ antibacterial activity has garnered a lot of attention because of their unique bactericidal processes, which include their capacity to interact with bacterial surfaces and penetrate the bacterial core, where they enter the cell [29]. The biological benefits of pomegranate peel can be harnessed using ZnO-NPs synthesised using this fruit’s extract. The inherent antibacterial characteristic of zinc gives the ZnO-NPs improved antibacterial and antimicrobial capabilities.  
The objectives of this study were: to synthesize ZnO nanoparticles via a green, cost-effective route using pomegranate peel extract as a reducing and stabilizing agent and characterize it using different methods, and to evaluate their antibacterial efficacy against multidrug-resistant clinical isolates.

MATERIALS AND METHODS
Chemicals and Instruments
All chemicals employed in the synthesis and analytical methods were rated as analytical reagent (AR) quality and utilised without additional purification except if specified differently. Zinc nitrate hexahydrate [Zn(NO₃)₂·6H₂O; CAS No. 10196-18-6; M.Wt. = 297.49 g/mol; catalogue No. 695595; minimum assay ≥99.0% (complexometric); pH of 10% aqueous solution: 3–6; CDH Fine Chemicals, Delhi, India] was utilized as the zinc precursor for nanoparticle manufacturing. The chemical is characterized as colorless or white crystals, readily soluble in water, producing a clear, colorless solution. Deionized water was utilized as the solvent in all preparatory stages. Ethanol (Duksan, Korea) was utilized for the washing and purifying of the resulting nanoparticle precipitate. Mueller–Hinton agar (Accumix/Oxoid, UK) served as the culture media for bacterial antimicrobial tests. The whole list of instruments and the requirements specified are presented in Tables 1 and 2.

Preparation of Pomegranate Peel Extract
Fresh pomegranates fruits (Punica granatum L.) were obtained from a nearby commercial supplier. After physically removing the peels from the fruit, they were washed with distilled water to remove any surface impurities. After that they were dried in a convection oven at 60°C until they reached a stable weight. Afterwards, a laboratory grinder was used to ground the dried peels into a fine powder.
For the extraction process, ten grams of dried peel powder were added to a 250 mL Erlenmeyer flask that already contained 200 mL of distilled water. Phytoconstituent extraction was ensured by subjecting the mixture to a hot-plate magnetic stirrer and heating it to 80°C while stirring constantly for 15 minutes. The conical-shaped Whatman No. 1 filter paper was used to filter the resulting dark orange-brown suspension. A glass funnel was placed in the funnel and held in place on a retort stand with a metal clamp. A 250 mL glass beaker was used to collect the filtrate. 
The clear, pale yellow to light greenish filtrate showed that insoluble peel residue was removed. To clarify the extract and remove microscopic particles, the filtrate was centrifuged at 1500 r/min. The refined pomegranate peel extract was stored at 5°C until nanoparticle production.

Green Synthesis of ZnO Nanoparticles
A 1 M stock solution of zinc nitrate hexahydrate [Zn(NO₃)₂·6H₂O/ CDH Fine Chemicals, India/ CAS No. 10196-18-6; Molecular Weight = 297.49 g/mol; purity ≥99.0% AR] was formulated by dissolving 59.49 g of the salt, calculated using the formula: wt = M × M.Wt × V = 1 mol/L × 297.49 g/mol × 0.200 L, in 200 mL of distilled water. The solution was transferred to a flask and magnetically stirred for 15 minutes at ambient temperature to complete dissolution, yielding a clear, colorless solution that matches the molecule’s solubility profile.
Pomegranate peel extract was slowly added to zinc nitrate while magnetically swirling to synthesize nanoparticles. The extract worked as both a bio-reducing and surface-capping agent, transforming Zn ⁺ ions into Zinc Oxide nuclei. A color change indicated nanoparticle formation after constant agitation. Allowing the reaction to finish.
Ultra Violet visible spectroscopy investigation confirmed the generation of Zinc Oxide nanoparticles by showing a unique absorption peak at 301 nm for the synthesized Zinc Oxide Nanoparticles solution, compared to 374 nm for the pomegranate peel extract. The blue shift concerning the extracted peak and the deviation from the bulk ZnO band edge (~380 nm) validated the development of nanoscale ZnO. The theoretical maximum concentration of ZnO in the final solution was determined under the assumption of complete conversion of Zn+2 to ZnO: 

L × 81.38 g/mol = 16.276 g. ZnO concentration = 16.276 g / 0.200 L = 81.38 g/L = 81.38 mg/mL (100% stock, Sample E).

moles = C × V = 1 mol/L × 0.200 L = 0.200 mol ZnO mass = moles × M.Wt = 0.200 × 81.38 = 16.276 g

After nanoparticle synthesis, the suspension underwent centrifugation to precipitate the nanoparticles and eliminate unreacted precursors and residual organic contaminants. The particle was progressively washed with distilled water and ethanol, then resuspended in distilled water to produce a purified ZnO-NP stock suspension at a theoretical concentration of 81.38 mg/mL. Serial dilutions of the stock solution (50%, 25%, and 12.5%) were produced in distilled water immediately before antibacterial examination (Table 3).

Bacterial Isolates and Culture Conditions
Multidrug-resistant (MDR) clinical isolates of Staphylococcus aureus (Gram-positive), Acinetobacter baumannii (Gram-negative), and Klebsiella pneumoniae (Gram-negative) were procured from Microbiology Laboratory of Ibn Al-Quff Hospital, Baghdad, Iraq. The multidrug-resistant (MDR) phenotype of each isolate was validated using conventional antimicrobial susceptibility testing utilizing the modified Kirby–Bauer disc diffusion method in accordance with the Clinical and Laboratory Standards Institute recommendations [30]. Stock cultures were preserved on nutrient agar slopes at 4°C and subcultured onto suitable media before each of the experiments.

Preparation of Culture Media
Mueller–Hinton agar (MHA; Oxoid, UK) was formulated according to the manufacturer’s guidelines. 38 grams of the dried powder were dissolved in one liter of distilled water. The suspension was heated with constant agitation on a hob until the powder was all dissolved. The medium was then sterilized using autoclaving at 121°C for 15 minutes. After autoclaving, the medium was permitted to cool to roughly 50°C in a water bath, after which approximately 20 mL was aseptically transferred onto sterile 90 mm polystyrene Petri plates. Plates were positioned on a flat surface for about 15 minutes to facilitate solidification, thereafter, inverted and stored at 4°C until required.

Antibacterial Activity Assay
The inoculum was made from overnight nutrient agar cultures of all bacterial isolates. Inoculated morphologically symmetrical colonies into 3 mL of sterile normal saline via a sterile wire loop. Turbidity was measured to 0.5 McFarland standard (1*108 CFU/mL) using a Densichek turbidity meter (bioMerieux, France). The inoculum sued within 15 minutes of manufacture.
Zinc Oxide Nanoparticles samples were tested for antibacterial activity using the modified agar well-diffusion method [30]. After cooling, 20 mL of molten MHA was poured into sterile Petri dishes to solidify. A sterile brush was immersed in the usual bacterial mixture and pressed against the tube wall to remove excess fluid to infect each plate. To ensure even coverage the swab was spread throughout the agar surface in three directions and turned 60° after each application. The swab was then put to the agar’s inner perimeter. To desiccate inoculated plates they were kept at room temperature for three minutes with closed lids.
With a sterile bio pette tip, 6 mm wells were formed in the agar. Each well was carefully filled with 50 microliters of Zinc Oxide Nanoparticles (Samples B, C, D, or E) or distilled water (Sample A (negative control)). In aerobic conditions plates incubated at 37°C for 18 to 24 hours. Incubation was followed by millimeter measurements of the zone of inhibition (ZOI) surrounding each well with a calibrated ruler. 
Following recognized breakpoints, the modified Kirby Bauer disc diffusion method [30] was used to assess the isolates antibiotic susceptibility [31]. As previously described MHA plates were infected with 0.5McFarland bacterial suspensions. 
Commercial antibiotic discs were placed on the inoculated agar surface using sterile forceps, pushed lightly to ensure total contact and incubated at 37°C for 18 to 24 hours.ZOI were measured and classed as sensitive, moderate or resistant [31]. Only MDR isolates were tested for ZO Nanoparticles.

RESULTS AND DISCUSSION
UV visible Spectroscopy
The absorption spectra of the synthesized ZnO sample had an absorption peak at 301 nm, while the pomegranate peel extract had a peak at 373 nm. This suggests that the electronic environment underwent a substantial change after interacting with zinc ions and forming a new nanophase. The blue shift can be ascribed to the reduced nanoscale dimensions the increased ratio of surface atoms and the influence of plantderived compounds on the particle surface. The absorption peak at 301 nm is markedly blueshifted relative to both the pomegranate peel extract and the approximately 380 nm band edge of bulk ZnO signifying a hypochromic shift associated with nanoscale size reduction. As particle dimensions decrease quantum confinement raises the effective band gap and shifts the absorption start to shorter wavelengths. Thus the optical response supports the idea that the synthesized ZnO was nanoscale. The 301 nm peak shows that the organic surface layer didn’t merely encapsulate ZnO but actively limited particle development during nucleation and stabilization [32-34]. 
The optical band gap from the Tauc plot (Eg=3.78 eV) confirms this perspective, as it greatly exceeds bulk ZnO, confirming the nanoscale band gap increase (Fig. 2). The TEM-derived particle size range of 4 to 8 nm implies that synthesized ZnO nanoparticles have a broader band gap aligning with quantum-confined nanostructure dimensions and optical properties rather than bulk like ZnO [34]. 

X-Ray Diffraction (XRD) 
The diffraction peaks showed peaks at 2θ = 31.77°, 34.42°, 36.25°, 47.54°, 56.60°, 62.86°, 66.38°, 67.96°, 69.10°, 72.56°, and 76.95° were assigned to the (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), and (202) planes of hexagonal wurtzite ZnO, aligning well with standard JCPDS/PDF card No. 36-1451 [35, 36].
Conversely specific XRD peaks at about 31.6, 34.3 and 36.0 among others indicate the hexagonal wurtzite structure of ZnO showing that the synthesized substance is nanocrystalline zinc oxide and an organometallic complex. 
The product’s phase purity and crystallinity were verified by XRD. The absence of extraneous diffraction peaks rules out phase contamination by zinc hydroxide or unreacted precursor, confirming that the product is phase pure crystalline ZnO[37]. 
The Debye Scherrer equation was used to calculate the average crystallite size of synthesized ZnOnanoparticles from XRD peaks [38]. The analyzed reflections had crystallite sizes ranging from 4.6 to 27.4 nm, with an average of 11 nm. 
This value matches the nanoscale domain, giving independent diffraction-based confirmation that the synthesized material comprises crystalline ZnO domains restricted to the lower nanoscale range. The comparatively wide FWHM values noted in most reflections smaller coherent scattering domains increase peak broadening in accordance with the Scherrer equation, as shown for green synthesized ZnO nanoparticles of similar dimensions derived from polyphenol rich plant extracts. 
According to the literature plant derived ZnO has an absorption edge in the UV spectrum due to its crystalline wurtzite structure and aggregated spherical or quasi spherical shape. This work found similar patterns [39].

Transmission Electron Microscopy (TEM) and Particle Size Distribution
Transmission Electron Microscopy images as in Fig. 3, showed that the green synthesized zinc oxide from pomegranate peel extract contains ultrafine nanoparticles with dimensions near the quantum-confinement regime, quasi spherical to irregular quasispheroidal shapes, and a propensity for secondary agglomeration. At 100 nm low magnification photos show condensed nano agglomerations in an inhomogeneous arrangement but at 20 and 10 nm these agglomerations are made of much smaller primary units packed tightly within nanoclusters.
Particle size spans from 4 to 8 nm with significant concentration at 5 ± 2 nm. Quantitative size analysis using TEM micrographs showed a mean diameter of 4.09±1.88 nm and a median of 2.98 nm with many particles in the 2 to 4 nm range and most of the material in the 2 to 8 nm range, indicating that the synthesized nanoparticles are in the quantum confinement domain of ZnO.
Pomegranate peel phytoconstituents excellent surface passivation during nucleation stops crystal growth early and promotes a very small primary particle population as shown by the right skewed distribution profile. Green route ZnO synthesis often uses plant based reducing agents and has a two tiered design with discrete ultrasmall primary units merged into loose secondary clusters. This morphological style is characterized by green ZnO synthesis which has a high surface energy and dipole nature. 
The remaining plant derived compounds on the surface form tiny primary units that form secondary clusters. The tendency for secondary agglomeration is due to ZnO high surface energy and polar wurtzite lattice, which encourage particle particle attraction after nucleation.
Similar structures have been seen in green synthesized ZnO using Punica granatum extract with various degrees of aggregation. However, the study particles are smaller and more densely aggregated [40]. 
The mean diameter from direct TEM measurements matches crystallite sizes from Debye Scherrer analysis of XRD peak broadening independently validating that TEM micrographs show coherent crystalline domains. Keeping those clusters extremely small primary units preserves the material’s biologically functional high surface to volume ratio.

Fourier Transform Infrared Spectroscopy
It was confirmed FTIR results morphological interpretation with broad bands in the 3248-3498 cm-1 range indicating hydroxyl groups, likely polyphenols and tannins in pomegranate peel. 
Conversely, the bands at 1622-1741 cm-1 align with plant extract carbonyl groups and organic chemicals, as well as flavonoids and organic acids maintained on the nanoparticle surface post synthesis, bonds between carbon and oxygen in the bands at 1141 and 1006 cm-1 support the organic coating idea, whereas the peculiar band at 451 cm-1 confirms zincand oxygen bonding and lattice vibration [41, 42].
Thus, TEM provides direct morphological evidence that supports the structural findings from XRD, the optical results from UV, and the chemical analysis from FTIR validating the green production of ZnO nanoparticles using pomegranate peel extract. The convergence analysis of XRD, TEM, UV visible, and FTIR validates the green manufacture of crystalline ZnO nanoparticles with pomegranate derived phytoconstituents.

Structure–Activity Relationship
Research shows that phenolic and organic compounds in pomegranate peel extract not only reduced synthesis but also partially coated and stabilized nanoparticle surfaces creating a durable organic corona close closeness of tiny particles. 
Transmission Electron Microscopy images show that surface organic molecules reduce crystal growth and sterically inhibit crystallite coalescence, while ZnO’s high surface energy and polarity drive secondary agglomeration. The data of FTIR show that ZnO was successfully synthesized and that nanoparticles in TEM micrographs are ultrafine primary units grouped into nanoclusters a hallmark of green synthesized nanomaterials. 
This organic corona may increase nanoparticle dispersibility in aqueous biological settings and electrostatic interactions with bacterial cell membranes, contributing to their antibacterial activity [41].
The antibacterial activity of synthesized ZnO is closely related to this nanostructure. The smaller primary particle size and increased specific surface area promote direct interaction with the bacterial cell.
They stimulate Zn+2 ions release and the formation of reactive oxygen species (ROS), which are critical mechanisms that affect permeability of the membrane induce oxidative stress and impede metabolic processes in bacterial cells.
Similarly, the presence of permanent surface organic groups, as demonstrated byFTIR, may enhance the stability of nanoparticles, and improve their interaction with the biological milieu. 
The formation of ultra fine ZnO particles aggregated into nanoclusters, as depicted in TEM micrographs, should not be viewed as a structural flaw, but rather as a deliberate morphological configuration conducive to enhanced biological efficacy against clinically significant multidrug-resistant pathogens. 
Thus, TEM, UV visible, FTIR and XRD results strongly suggest that pomegranate peel extract reduced and stabilized nanoparticles and formed bioactive and crystalline small sized nano ZnO making it an attractive option for hospital infection prevention [43,44].

Antibacterial activity of ZnO-NPs 
All three trials show a dose dependent relationship. From 12.5% (B) to 100% (E), ZnO nanoparticle concentration increases the Zone of Inhibition (ZOI). Sample A (Control) shows little to no inhibition demonstrating that distilled water is not antibacterial and that the nanoparticles are the only factor. Sample E (100%) consistently has the maximum ZOI indicating excellent efficacy at maximal concentration.
The nanoparticles eliminate Gram-positive S. aureus and Gram-negative A. baumannii, K. pneumoniae bacteria, but sensitivity varies. At 100% concentration (81.38 mg/ml), S. aureus showed a 44 mm inhibitory zone bigger than the others. Even at low doses 12.5% maintained a 30 mm zone of inhibition. 
A. baumannii displays slightly higher sensitivity than K. pneumoniae, reaching approximately 28 mm at 100% concentration. As illustrated in Figs. 4-6, K. pneumoniae displays ZOI ranging from approximately 16 mm (12.5%) to 24 mm (100%).
The study found that ZnO nanoparticles concentrations enhance the ZOI. S. aureus is highly susceptible to green-synthesized ZnO nanoparticles. Gram positive bacteria lack the outer lipopolysaccharide (LPS) membrane of Gram negative bacteria, making them more susceptible to nanoparticle invasion. These strains are notoriously multi drug resistant. Gram positive bacteria lack an exterior protective barrier but have a strong, permeable peptidoglycan layer. 
This arrangement improves ZnO nanoparticle cell penetration. Premanathan et al. (2011) found that Gram positive bacteria are more susceptible to ZnO nanoparticles due to their negative cell walls, which attract positively charged Zn²⁺ ions and cause membrane damage. The fact that ZnO nanoparticles have different zones beyond 20 mm suggests they can fight these robust illnesses [45].
baumannii and K. pneumoniae have smaller inhibitory zones (16 to 28 mm). Gram negative bacteria have greater resistance to the LPS membrane, according to the literature. Nanoparticles can’t enter the cytoplasm through this membrane’s chemical barrier. A. baumannii is resistant to traditional antibiotics, however metal oxide nanoparticles can physically break the cell membrane and bypass resistance mechanisms like efflux pumps [46].
Many Klebsiella bacteria create a capsular polysaccharide that “trap” nanoparticles and impede their passage to the cell membrane, which may explain K. pneumoniae lower sensitivity this physical entrapment process adds resistance beyond the outer membrane barrier and may explain the decreased ZOI levels compared to other strains. This matches the results correspond with the observations of Rizwan et al. (2010), and Alekish et al. (2025), who found that high nanoparticle concentrations increase reactive oxygen species (ROS), which damage bacterial DNA and proteins or disrupt cell walls by aggregating on the bacterial surface and “pitting” the cell wall [47, 48]. Alternatively, Zn+2 ions may enter the cell and disturb metabolism. Nanoparticle cell wall interactions grow with concentration, causing oxidative stress and cell death. 
The phytochemical components of the pomegranate peel extract preserved on the nanoparticle surface by FTIR, are known to have antibacterial activities and may improve the zinc oxide core’s inhibitory effectiveness. This synergistic method may enhance the antibacterial activity of nanoparticles containing plant bioactive compounds such as flavonoids and polyphenols compared to chemically synthesized ZnO [32]. 

CONCLUSION
In this study, bioactive ZnO NPs were synthesized by eco friendly approach using pomegranate peel extract. Detailed characterization confirmed the presence of crystalline ultra fine nanoparticles ~4-8 nm that stabilized by organic layer of phytochemicals derivedfrom plants. The synthesized ZnO NPs showed a marked dose dependent antibacterial activity against clinically relevant MDR pathogens; S. aureus, A. baumannii, and K. pneumoniae. Bacterial cell wall composition affects activity of NPs as indicated by higher sensitivity of Gram positive S. aureus strains as compared to Gram negative strains. The organic corona made from pomegranates and the zinc oxide core synergistically improve the biological performance of nanostructures, which enhance the intrinsic antibacterial properties of the core to resist antibiotic resistance and address the urgent need for new therapies in clinical applications. The results indicate that ZnO nanoparticles synthesized by green synthesis are an effective, practical and environment friendly solution.

CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.