Biogenic Gold Nanoparticles Decrease Methylene Blue Photobleaching and Enhance Antimicrobial Photodynamic Therapy.

Irena Maliszewska,Ewelina Wanarska,Alex C Thompson,Ifor D W Samuel,Katarzyna Matczyszyn

doi:10.3390/molecules26030623

Abstract

Antibiotic resistance is a growing concern that is driving the exploration of alternative ways of killing bacteria. Here we show that gold nanoparticles synthesized by the mycelium of Mucor plumbeus are an effective medium for antimicrobial photodynamic therapy (PDT). These particles are spherical in shape, uniformly distributed without any significant agglomeration, and show a single plasmon band at 522–523 nm. The nanoparticle sizes range from 13 to 25 nm, and possess an average size of 17 ± 4 nm. In PDT, light (from a source consisting of nine LEDs with a peak wavelength of 640 nm and FWMH 20 nm arranged in a 3 × 3 array), a photosensitiser (methylene blue), and oxygen are used to kill undesired cells. We show that the biogenic nanoparticles enhance the effectiveness of the photosensitiser, methylene blue, and so can be used to kill both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The enhanced effectiveness means that we could kill these bacteria with a simple, small LED-based light source. We show that the biogenic gold nanoparticles prevent fast photobleaching, thereby enhancing the photoactivity of the methylene blue (MB) molecules and their bactericidal effect.

Highlights

The risk of infection in patients from contaminated areas has been discussed in healthcare for many years
In this paper we show how biogenic gold nanoparticles can lead to effective antimicrobial PDT (aPDT) of both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria
Under the conditions defined in our studies we found that antimicrobial photodynamic therapy (PDT) in vitro reduces the concentration of Staphylococcus aureus and Escherichia coli viable cells, and that this process is enhanced by biogenic gold nanoparticles

Summary

Introduction

The risk of infection in patients from contaminated areas has been discussed in healthcare for many years. It is known that the environment is a key source of hospital pathogens [2], attention has been focussed on the disinfection of hospitals, in particular using antibacterial treatments carried out in novel ways, including antibacterial light sources [3,4,5]. Such new strategies, capable of decontaminating both patient wounds and the environment, are important tools for the fight against dangerous hospital pathogens. It is well established for the treatment of several cancers, and has been successfully employed for the treatment of skin tumours [5,6], cutaneous T-cell lymphoma [7], and tumors localized in the oral cavity and tongue [8,9]

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