The Activity of Gold Nanoparticles Synthesized Using Helichrysum odoratissimum Against Cutibacterium acnes Biofilms.

Marco Nuno De Canha,Kattesh V Katti,Vusani Mandiwana,Rirhandzu Rikhotso,Michel Lonji Kalombo,Namrita Lall,Suprakas Sinha Ray,Arno Janse Van Vuuren,Velaphi Clement Thipe

doi:10.3389/fcell.2021.675064

Abstract

The human skin is home to millions of bacteria, fungi, and viruses which form part of a unique microbiome. Commensal microbes, including Cutibacterium acnes can occasionally become opportunistic resulting in the onset of dermatological diseases such as acne. Acne is defined as a chronic inflammatory disorder based on its ability to persist for long periods throughout an individual’s life. The synthesis of gold nanoparticles (AuNPs) was performed using the bottom-up approach by reduction of a gold salt (HAuCl4.3H2O) by the methanol extract (HO-MeOH) and aqueous decoction prepared from the dried aerial parts of Helichrysum odoratissimum (HO-Powder). The HO-MeOH and HO-Powder AuNPs were prepared as unstabilised (−GA) or stabilized (+GA) by the omission or addition of Gum Arabic (GA) as the capping agent. The characterization of the AuNPs was performed using Transmission Electron Microscopy (TEM), dynamic light scattering (DLS), Ultraviolet-Visual spectroscopy (UV-Vis), Thermogravimetric Analysis (TGA), X-Ray Diffraction (XRD) and Zeta-potential. The MBIC50 values for HO-MeOH − GA and HO-MeOH + GA were 1.79 ± 0.78% v/v and 0.22 ± 0.16% v/v, respectively. The HO-Powder AuNPs showed potent inhibition of C. acnes cell adhesion to the 96-well plates. The HO-MeOH − GA and HO-Powder + GA exhibited IC50 of 22.01 ± 6.13% v/v and 11.78 ± 1.78% v/v, respectively. The activity of the AuNPs validated the anti-adhesion activity of the methanol extract in the crude form. The study emphasizes the selectivity of H. odoratissimum AuNPs for the prevention of C. acnes cell adhesion and not antimicrobial activity, which may prevent the emergence of resistant strains of C. acnes through reduced bactericidal or bacteriostatic activity, while targeting mechanisms of pathogenesis.

Highlights

The human skin is a host to numerous species of bacteria, fungi, and viruses; each with their own optimal micro-environment
The synthesis of gold nanoparticles using both the dried plant material and the methanol extract of Helichrysum odoratissimum resulted in the reduction of the gold salt
The use of H. odoratissimum in the nanoparticle form exhibited similar anti-biofilm activity when compared to the biological activity of the methanol extract as previously reported by De Canha et al (2020)

Summary

Introduction

The human skin is a host to numerous species of bacteria, fungi, and viruses; each with their own optimal micro-environment. Differences in skin physiology, including oil content, moisture content or absence thereof, have a large influence on the variability of microbial species These microorganisms have essential functions as protectors against invasive pathogens, inducers of immune responses, and metabolizers of natural products. To overcome barrier function for enhanced permeation and delivery of these natural ingredients, many studies have investigated the use of nanotechnology, in particular the use of colloidal gold, for the green synthesis of gold nanoparticles (AuNPs) The surface of these nanoparticles is rapidly modified with the addition of chemical compounds or other bioactive molecules (Gupta and Rai, 2016). The study aimed to determine whether the AuNPs synthesized using H. odoratissimum would show similar antimicrobial and anti-biofilm activity when compared to that of the extract alone, which was previously reported by De Canha et al (2020)

Methods

Results

Conclusion