Gold nanoparticles in an enhancement of antimicrobial activity

Abstract

The effect of antimicrobial photodynamic therapy (aPDT) on Gram-positive bacterium Staphylocccus aureus was studied. Methylene blue (MB) at non-toxic concentration of 31.25µg/ml was used as a photosensitizer. LEDs diodes were used as a light source to study the effect of methylene blue alone and the MB-gold nanoparticle mixture on the viability of S. aureus cells. Biogenic gold nanoparticles (biolAuNPs, 10ppm) and chemically synthesized gold nanoparticles (chemAuNPs, 3ppm) were tested as enhancement agents. In the presence of MB alone as a photosensitizer, the killing effect was about 92% after 30min of irradiation. The aPDT therapy was enhanced by addition of biolAuNPs and chemAuNPs and killing rate of S. aureus was 95-96% after 30min of irradiation. The probable mechanism of enhancement of MB-mediated photodynamic bactericidal efficacy against S. aureus in the presence of gold nanoparticles is discussed leading to the conclusion that colloidal gold increases the accumulation of MB in bacterial cells.

Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies

“…Moreover, gold NPs display biocompatibility, low toxicity, and immunogenicity, almost chemical inertness (distinctly from their inherent catalytic properties), while silver nanomaterials present intrinsic antimicrobial activity against a broad spectrum of microorganisms and related MDR infections (e.g., towards Gram(−) and Gram(+) mature biofilms of MRSA), and disruption of biofilm formations while being safe for mammalian cells [124][125][126].Ultimately, both Au and Ag NPs share nano features specific to noble metal systems, i.e., localized surface plasmon resonance (LSPR, arising from their resonant oscillation of their free electrons upon light exposure) and resonance energy transfer (RET), with subsequent optical and photothermal properties of enhancing appositeness in aPDT applications and PDI efficacy (e.g., ROS production) [127][128][129]. For the most part, Au and Ag NPs of various shapes (e.g., spheres, rods, cubes) are combined with organic PS molecules such as RB and MB [128][129][130][131][132][133][134][135][136], but also with metallated PSs such as ruthenium complexes, metallophthalocyanines, and metalloporphyrins [108,137,138]; the corresponding PS nanovehicles can also be labeled as "conjugates" but they strictly differ from the "mixtures" involving metal NPs and PS molecules [139]. Other noble metal NPs, viz., platinum, have also been employed in aPDT applications due to their multitarget action to inactivate microbes, although to a lower degree up to now owing to synthetic limitations [27,140].…”