Original Article
Zinc oxide nanoparticle suspensions and layer-by-layer coatings inhibit staphylococcal growth

https://doi.org/10.1016/j.nano.2015.10.002Get rights and content

Abstract

Despite a decade of engineering and process improvements, bacterial infection remains the primary threat to implanted medical devices. Zinc oxide nanoparticles (ZnO-NPs) have demonstrated antimicrobial properties. Their microbial selectivity, stability, ease of production, and low cost make them attractive alternatives to silver NPs or antimicrobial peptides. Here we sought to (1) determine the relative efficacy of ZnO-NPs on planktonic growth of medically relevant pathogens; (2) establish the role of bacterial surface chemistry on ZnO-NP effectiveness; (3) evaluate NP shape as a factor in the dose–response; and (4) evaluate layer-by-layer (LBL) ZnO-NP surface coatings on biofilm growth. ZnO-NPs inhibited bacterial growth in a shape-dependent manner not previously seen or predicted. Pyramid shaped particles were the most effective and contrary to previous work, larger particles were more effective than smaller particles. Differential susceptibility of pathogens may be related to their surface hydrophobicity. LBL ZnO-NO coatings reduced staphylococcal biofilm burden by > 95%.

From the Clinical Editor

The use of medical implants is widespread. However, bacterial colonization remains a major concern. In this article, the authors investigated the use of zinc oxide nanoparticles (ZnO-NPs) to prevent bacterial infection. They showed in their experiments that ZnO-NPs significantly inhibited bacterial growth. This work may present a new alternative in using ZnO-NPs in medical devices.

Graphical abstract

Despite a decade of engineering and process improvements, bacterial colonization and infection remain the primary threats to implanted medical devices. Zinc oxide nanoparticles (ZnO-NPs) are attractive alternatives to silver NPs or antimicrobial peptides for device coatings to prevent infection. Here we address several questions regarding ZnO-NPs and their interactions with bacteria in an effort to translate this material toward antibacterial medical device coatings. Using a Layer-by-layer technique we demonstrate that ZnO-NP coatings reduce staphylococcal biofilm burden by > 95%.

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Section snippets

Bacterial strains, media, and growth conditions

The bacterial strains used in this study were Escherichia coli UTI89 and MG1655, Klebsiella pneumoniae LM21, methicillin-resistant Staphylococcus aureus SH1000, and Staphylococcus epidermidis RP62A. Glycerol stocks of all strains maintained at − 80 °C were plated on tryptic soy agar, cultured overnight at 37 °C and stored at 4 °C. Single colony inoculates were grown in tryptic soy broth + 1% glucose w/v (TSBG) under shaking conditions for 16 h at 30 °C and diluted 1:50 for planktonic growth curves and

Results

In this study, we considered three ZnO-NP geometries: plates, spheres, and pyramids. The edges of the hexagonal base of pyramids were ~ 20 nm, while their side edges were ~ 25 nm (Figure 1, A). The diameter of spheres was ~ 4.4 nm (Figure 1, B). The diameter and thickness of plates were ~ 20 nm and ~ 3.5 nm, respectively (Figure 1, C & Supplemental Figure S2). Despite the obvious differences in the shape of the NPs, the crystals’ structures were nearly identical and all diffraction rings could be matched

Discussion

ZnO-NPs are a potential new antimicrobial technology with many features which make them an attractive alternative to silver or antimicrobial peptides for preventing medical device infection. In this study, we synthesized ZnO-NPs into three distinct shapes without the use of traditional surfactants or capping agents. This feature of our synthesis process is significant in light of the potential for these additional molecules to confound the results of experiments. As such, we were able to

Acknowledgments

The authors would like to thank Gleiciani de Queiros Silverira for her help with identification of electron diffraction rings for crystalline ZnO, Usha Kadiyala for her assistance completing the quantitative culture of S. aureus, and Siu On Tung for his assistance with obtaining FTIR spectra.

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      ZnO NP coated glass slide showed bactericidal activity against E. coli. Layer-by-layer coating of ZnO NPs on a polystyrene 96 well plate inhibited the biofilm formation of Staphylococcus sp. [92]. ZnO NPs with a sol-gel coating on 96 well microtiter plate (polystyrene material) inhibited up to 89.2% of P. otitidis biofilm formation [93].

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    Conflict of interest/funding: This work is partially supported by a Research Training Grant (RF2013-002) from the Society for Academic Emergency Medicine, National Institutes of Health Grant NIGMS RO1 GM081702, U.S. Army Research Office Grant Award No. W911NF-10-1-0518, and AFOSR Grant Award No. MURI W911NF-12-1-0407. We acknowledge support from the National Science Foundation under grant ECS-0601345; CBET 0933384; CBET 0932823; and CBET 1036672. The authors have no competing conflicts of interest related to this work.

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    These authors contributed equally.

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