ZnO Nanoparticles-Modified Dressings to Inhibit Wound Pathogens

Abstract

Zinc oxide (ZnO) nanoparticles (NPs) have been investigated for various skin therapies in recent years. These NPs can improve the healing and modulate inflammation in the wounds, but the mechanisms involved in such changes are yet to be known. In this study, we have designed a facile ZnO nano-coated dressing with improved antimicrobial efficiency against typical wound pathogens involved in biofilm and chronic infections. ZnO NPs were obtained by hydrothermal method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. Antibacterial and antibiofilm effects were evaluated against laboratory and clinical isolates of significant Gram-negative (Pseudomonas aeruginosa and Escherichia coli) and Gram-positive (Staphylococcus aureus and Enterococcus faecalis) opportunistic pathogens, by quantitative methods. Our results have shown that the developed dressings have a high antibacterial efficiency after 6-24 h of contact when containing 0.6 and 0.9% ZnO NPs and this effect is similar against reference and clinical isolates. Moreover, biofilm development is significantly impaired for up to three days of contact, depending on the NPs load and microbial species. These results show that ZnO-coated dressings prevent biofilm development of main wound pathogens and represent efficient candidates for developing bioactive dressings to fight chronic wounds.

Keywords: ZnO nano-coatings; antimicrobial nanoparticles; biofilm control; chronic wounds; opportunistic pathogens.

Figure 1

SEM images of the ZnO NPs-coated dressings (ZnO 0.3%; 0.6%; 0.9%) at various similar magnification ((a1–a3) = scale is 300 µm, (b1–b3) = scale is 30 µm, (c1–b3) = scale is 10 µm).

Figure 1

SEM images of the ZnO NPs-coated dressings (ZnO 0.3%; 0.6%; 0.9%) at various similar magnification ((a1–a3) = scale is 300 µm, (b1–b3) = scale is 30 µm, (c1–b3) = scale is 10 µm).

Figure 2

TEM images of the obtained ZnO NPs: (a) brigh-field; (b) HR-TEM and (c) SAED pattern.

Figure 3

FT-IR spectra for control and for the ZnO NPs-coated dressings (ZnO 0.3; 0.6; 0.9%) and control.

Figure 4

XRD spectra of ZnO NPs-coated dressings (ZnO 0.3; 0.6; 0.9%).

Figure 5

Graphical representation of log10 CFU/mL values obtained for the Gram-positive tested microbial strains (three S. aureus (S.a.) = (A) and 2 E. faecalis (E.f.) isolates = (B)), expressing viability of bacteria incubated as 0.5 McFarland suspensions in PBS on the ZnO NPs-coated wound dressings for 1 h, 6 h, 12 h, and 24 h (* p < 0.05; ** p < 0.001; *** p < 0.0001 by comparing viability on control coatings with ZnO-coated dressings).

Figure 6

Graphical representation of log10 CFU/mL values obtained for the Gram-negative tested microbial strains (2 E. coli (E.c.) = (A) and 3 P. aeruginosa (P.a.) isolates = (B)), expressing viability of bacteria incubated as 0.5 McFarland suspensions in PBS on the ZnO NPs-coated wound dressings for 1 h, 6 h, 12 h, and 24 h (** p < 0.001; *** p < 0.0001 by comparing viability on control coatings with ZnO-coated dressings).

Figure 7

Graphic representation of average absorbances at 600 nm revealing growth of planktonic microbial cultures in the presence of control and nano-coated dressings for 24 h at 37 °C (* p < 0.05 by comparing average Abs 600 nm of all strains of the analyzed species growth in the presence of control and ZnO NPs containing coatings).

Figure 8

Graphic representation of average log10 CFU/mL values obtained for the tested Gram-positive and Gram-negative microbial strains, expressing biofilm embedded cells developed on control and ZnO NPs-coated dressings for different time points (24 h, 48 h, 72 h) (* p < 0.05; ** p < 0.001 by comparing biofilm formation on control and each ZnO-coated dressings).