This research was supported by the Chung-Ang University Graduate Research Scholarship in 2022 (Ms. Gahyun Lee). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2020R1A5A1018052) and by the Technology development Program (RS202300261938) funded by the Ministry of SMEs and Startups (MSS, Korea).

The reagents and equipment used in this study are listed in the Table of Materials.
1. Preparation of zinc oxide nanoparticles
<ol>
	<li>Measure 200 mL of absolute ethyl alcohol and pour it into a glass round bottom flask.</li>
	<li>Place the round bottom flask on a heating mantle and maintain stirring at 25-40 &#176;C.</li>
	<li>Measure 500 mg of CTAB in a 50 mL vial and add it to the ethyl alcohol in the flask. Stir until CTAB is completely dissolved.</li>...

 Zinc Oxide Nanoparticles Synthesis and Analysis of its Antibacterial Effects

<ol>
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G., Kamble, V. B., Annsi, J. I., Sarma, L. S., Mahajan, C. 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K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+nano-ZnO+by+chemical+method+and+its+characterization.">Synthesis of nano-ZnO by chemical method and its characterization.</a> Results Chem. 5, 100771 (2023).</li><li>Choi, K. -. 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D., Kornowski, A., Weller, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Colloidal+synthesis+of+organic-capped+ZnO+nanocrystals+via+a+sequential+reduction-oxidation+reaction.">Colloidal synthesis of organic-capped ZnO nanocrystals via a sequential reduction-oxidation reaction.</a> J Phy Chem B. 109 (7), 2638-2644 (2005).</li><li>Roh, S., Jang, Y., Yoo, J., Seong, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+modification+strategies+for+biomedical+applications:+Enhancing+cell-biomaterial+interfaces+and+biochip+performances.">Surface modification strategies for biomedical applications: Enhancing cell-biomaterial interfaces and biochip performances.</a> BioChip J. 17, 1-18 (2023).</li><li>Chen, D., Jiao, X., Cheng, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrothermal+synthesis+of+zinc+oxide+powders+with+different+morphologies.">Hydrothermal synthesis of zinc oxide powders with different morphologies.</a> Solid State Commun. 113 (6), 363-366 (1999).</li><li>Hu, X. -. L., Zhu, Y. -. J., Wang, S. -. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sonochemical+and+microwave-assisted+synthesis+of+linked+single-crystalline+ZnO+rods.">Sonochemical and microwave-assisted synthesis of linked single-crystalline ZnO rods.</a> Mater Chem Phys. 88 (2-3), 421-426 (2004).</li><li>Ahamad Khan, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phytogenically+synthesized+zinc+oxide+nanoparticles+(ZnO-NPs)+potentially+inhibit+the+bacterial+pathogens:+In+vitro+studies.">Phytogenically synthesized zinc oxide nanoparticles (ZnO-NPs) potentially inhibit the bacterial pathogens: In vitro studies.</a> Toxics. 11 (5), 452 (2023).</li><li>Xie, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+advances+in+ZnO+nanomaterial-mediated+biological+applications+and+action+mechanisms.">Recent advances in ZnO nanomaterial-mediated biological applications and action mechanisms.</a> Nanomaterials. 13 (9), 1500 (2023).</li><li>Chawla, U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+on+ZnO-based+targeted+drug+delivery+system.">A review on ZnO-based targeted drug delivery system.</a> Lett Drug Des Discov. 21 (3), 397-420 (2024).</li><li>Alavi, M., Nokhodchi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+overview+on+antimicrobial+and+wound+healing+properties+of+ZnO+nanobiofilms,+hydrogels,+and+bionanocomposites+based+on+cellulose,+chitosan,+and+alginate+polymers.">An overview on antimicrobial and wound healing properties of ZnO nanobiofilms, hydrogels, and bionanocomposites based on cellulose, chitosan, and alginate polymers.</a> Carbohydr Polym. 227, 115349 (2020).</li></ol>

The synthesis of ZnO NPs via precipitation is relatively simple and straightforward. To successfully synthesize ZnO NPs using this method, stirring is crucial to ensure that the precursor (zinc acetate) is fully dissolved in the solvent. Moreover, increasing the temperature helps to induce a successful double-displacement reaction. In the synthesis of ZnO NPs, there are many factors that determine the size and shape, including the precipitation agent, the concentration of the precipitation agent, and the surfact...

Multidrug-resistant (MDR) bacterial infections pose a significant global threat to human health1. As these infections can be fatal in patients with underlying conditions, active research is attempting to address this issue2. Bacteria have evolved to evade the action of various drugs. Penicillin, widely known and credited with saving millions of lives worldwide, is a &#946;-lactam antibiotic that inhibits the synthesis of the bacterial cell wall3. However, bacteria have evolved to neutralize the efficacy of drugs through various mechanisms such as efflux pumps, transpeptidase alterations, or decreased permeability4. Additionally, bacterial cells can transmit these resistance genes to the next generation, increasing the survival rates of the subsequent generation and strengthening the problem of resistant strains5.
The increase in antibiotic-resistant bacteria has led to the emergence of MDR bacteria, which commonly exhibit resistance to multiple antibiotics. MDR strains are most frequently encountered in hospital settings, where multiple bacterial strains are exposed to and consequently develop resistance to different antibiotics6. Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA), is a gram-positive commensal bacterium that forms clusters on the skin of approximately 30% of humans7,8. MRSA, which was first identified in the 1960s, exhibits reduced sensitivity to &#946;-lactam antibiotics, resulting in a sharp increase in infection rates since the 1990s9. Among gram-negative bacteria, Pseudomonas aeruginosa (P. aeruginosa) is one of the most prevalent strains acquired in hospitals. This species, a facultative rod-shaped bacterium, causes opportunistic infections in humans10. Particularly, MDR strains that directly affect human health are responsible for over 50 % of healthcare-associated infections11. In this study, we utilized the most commonly encountered multidrug-resistant strains within hospitals, MRSA&#160;and P. aeruginosa.
The use of nanoparticles (NPs) for antimicrobial purposes has been extensively investigated to tackle the issue of antibiotic resistance. Metallic NPs, in particular, induce bacterial cell death through various mechanisms, offering a potential solution to the problem of drug resistance. Metallic NPs exert antimicrobial activity through multiple mechanisms, including the release of antimicrobial ions, generation of reactive oxygen species (ROS), and physical disruption of cells, among other means12. NPs composed of silver, copper, zinc oxide (ZnO), and titanium oxide possess high antimicrobial efficacy and are thus being actively researched13.
ZnO NPs have been approved by the U.S. Food and Drug Administration (FDA) for use in humans. Conversely, despite their high antimicrobial efficacy, the use of silver and copper NPs in humans is limited by their high cytotoxicity. However, ZnO NPs are commonly found in everyday life and are even present in widely used sunscreen formulations14. Of note, Zn2+ ions released from ZnO NPs are highly effective in bacterial treatment, inducing bacterial cell death through the generation of ROS and other physical damage mechanisms15.
This study outlines the protocol for synthesizing ZnO nanoparticles (NPs) using a precipitation method and introduces an antimicrobial testing approach using a microbroth dilution method with clinical samples of MRSA and P. aeruginosa. The precipitation method for ZnO NPs involves synthesizing insoluble solid ZnO NPs by adjusting pH and temperature using soluble precursors such as zinc acetate or zinc nitrate16. Along with relatively facile and rapid production, this method ensures repeatability in synthesis and facilitates control over particle size and morphology17. In this synthesis protocol, sodium hydroxide (NaOH), one of the most commonly used precipitation agents, was utilized to precipitate zinc acetate, and a small amount of hexadecyltrimethylammonium bromide (CTAB) was employed to inhibit the uncontrolled synthesis of the nanoparticles18. Among various antimicrobial tests, the antibacterial activity of ZnO nanoparticles was evaluated using the microbroth dilution method, which avoids optical interference from metal oxide nanoparticles and enables direct colony measurement for determining MIC19.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>DLS</td>
			<td>Zetasizer Pro</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl alcohol, absolute</td>
			<td>DAEJUNG</td>
			<td>4023-2304</td>
			<td></td>
		</tr>
		<tr>
			<td>Microplate reader&#160;</td>
			<td>BioTeck</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>221465</td>
			<td></td>
		</tr>
		<tr>
			<td>TEM</td>
			<td>JEOL JEM-F200</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>TSA</td>
			<td>DB difco</td>
			<td>236950</td>
			<td></td>
		</tr>
		<tr>
			<td>TSB</td>
			<td>DB difco</td>
			<td>211825</td>
			<td></td>
		</tr>
		<tr>
			<td>XRD</td>
			<td>NEW D8-Advance</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Zinc acetate</td>
			<td>Sigma-Aldrich</td>
			<td>383317</td>
			<td></td>
		</tr>
	</tbody>
</table>

preparation of zinc oxide nanoparticles and the evaluation of their antibacterial effects

Nosocomial bacterial infections have become increasingly challenging due to their inherent resistance to antibiotics. The emergence of multidrug-resistant bacterial strains in hospitals has been attributed to the extensive and varied use of antibiotics, further exacerbating the problem of antibiotic resistance. Metal nanomaterials have been widely studied as an alternative solution for eradicating antibiotic-resistant bacterial cells. Metallic nanoparticles attack bacterial cells through various mechanisms, such as the release of antibacterial ions, generation of reactive oxygen species, or physical disruption, against which bacteria cannot develop resistance. Among the actively researched antimicrobial metal nanoparticles, zinc oxide nanoparticles, which are FDA-approved, are known for their biocompatibility and antibacterial properties. In this study, we focused on successfully developing a precipitation method for synthesizing zinc oxide nanoparticles, analyzing the properties of these nanoparticles, and conducting antimicrobial tests. Zinc oxide nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), ultraviolet/visible spectroscopy, and X-ray diffraction (XRD). Antibacterial tests were conducted using the broth microdilution test with the multidrug-resistant strains of methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. This study demonstrated the potential of zinc oxide nanoparticles in inhibiting the proliferation of antibiotic-resistant bacteria.

Author Spotlight: Exploring the Antibacterial Effects of Zinc Oxide Nanoparticles in Overcoming Antibiotic Resistance

Preparation of Zinc Oxide Nanoparticles and the Evaluation of their Antibacterial Effects

Antibiotic-resistant bacterial infections are currently emerging as a global issue. To address this problem, we have focused on development of antibacterial metallic nanoparticles, employing various mechanisms to eradicate bacterial cells. Zinc oxide nanoparticles are known for their excellent antibacterial capabilities.As they're approved by the FDA, they're known to be biocompatible to the human body. The major advantage of our zinc oxide nanoparticle synthesis method lies in its simplicity and relatively short synthesizing time compared to other protocols, owing to its precipitation-based synthesis approach. This makes it a highly effective method, particularly for mass production from a commercialization perspective, and additionally, its chemical synthesis without the need for specialized equipment adds to its appeal as well.Our research team plans to further develop antibacterial therapy using zinc oxide nanoparticles or inorganic nanoparticles, and integrate them with drug delivery for real-world applications. To achieve more effective bacteria-specific treatment, we will utilize antibodies and lectins for targeting bacteria, minimizing general cell toxicity of particles, and conducting research on delivering particles to pathogens in actual infection environments.

The successful synthesis of ZnO NPs was confirmed using transmission electron microscopy (TEM), as shown in Figure 1A. The obtained ZnO NPs were observed to be round in shape, with an average particle size of 35.35 nm and a standard deviation of 6.81 nm. The precipitation of these nanoparticles was observed through a double-displacement reaction by adding NaOH solution to zinc acetate, where Zn2+ ions underwent hydrolysis.
Using dynamic light scattering...

In this study, zinc oxide nanoparticles were synthesized using a precipitation method. The antibacterial effect of the synthesized particles was tested against multidrug-resistant methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa bacterial strains.

Nosocomial bacterial infections have become increasingly challenging due to their inherent resistance to antibiotics. The emergence of multidrug-resistant ...

preparation-zinc-oxide-nanoparticles-evaluation-their-antibacterial