Antibacterial Activity and Cytotoxicity of Gold (I) and (III) Ions and Gold Nanoparticles

Abstract

Gold nanoparticles (AuNPs) and gold ion complexes have been investigated for their antibacterial activities. However, the majority of the reports failed to disclose the concentration of free Au(I) or Au(III) present in solutions of AuNPs or gold ion complexes. The inconsistency of antibacterial activity of AuNPs may be due to the effect of the presence of Au(III). Here we report the antibacterial activity of Au(I) and Au(III) to four different bacteria: one nonpathogenic bacterium: E. coli and three multidrug-resistant bacteria: E. coli, S. typhimurium DT104, and S. aureus. Au(I) and Au(III) as chloride are highly toxic to all the four bacteria, with IC50 of 0.35 – 0.49 µM for Au(III) and 0.27–0.52 µM for Au(I).The bacterial growth inhibition by both Au(I) and Au(III) increases with exposure time and is strongly affected by the use of buffers. The IC50 values for Au(I) and Au(III) in different buffers are HEPES (0.48 and 1.55 µM) > Trizma (0.41 and 0.57 µM) > PBS (0.14 and 0.06 µM). Bacterial growth inhibition by AuNPs is gradually reduced by centrifugation-resuspension to remove residual Au(III) ion present in the crude synthetic AuNPs. After 4 centrifugations-resuspensions, AuNPs become non-toxic. In addition, both Au(I) and Au(III) are cytotoxic to skin keratinocyte and blood lymphocyte cells. These results suggest that Au(I) and Au(III) in pure or complex forms may be explored as a method to treat drug-resistant bacteria, and the test of AuNPs toxicity must consider residual Au(III), exposure time, and the use of buffers.

Nano-Strategies to Fight Multidrug Resistant Bacteria—“A Battle of the Titans”

“…The most used and described method is the chemical synthesis based on the reduction of chloroauric acid by citrate (Lee and Meisel, 1982 ; Fernandes and Baptista, 2017 ). Some studies have addressed the potential of using AuNPs as antibacterial agents, but some controversy still exists (Cui et al, 2012 ; Bresee et al, 2014 ; Shah et al, 2014 ; Shareena Dasari et al, 2015 ; Zhang et al, 2015a ; Shamaila et al, 2016 ).…”

Synthesis and characterisation of cross-linked chitosan composites functionalised with silver and gold nanoparticles for antimicrobial applications

“…Further tests revealed that Au 3+ is the more dominant ion as the bacterial inhibition significantly reduced with gradual removal of Au 3+ ions. The cytotoxicity of Au 3+ increases with concentration, posing possible problems in vivo [ 52 ].…”

Magnetic and Golden Yogurts. Food as a Potential Nanomedicine Carrier

“…The ferment was incubated with a 1 mM gold salt solution (HAuCl 4 3H 2 O). An optimal incubation time was selected based on some previously published results which demonstrated that gold ions can act as antimicrobial agents at a concentration 1000 times less than the one we were using [37,38] and that they are toxic for bacterial strains such as Escherichia, Staphylococcus, and Salmonella [39]. Taking this into account, all our experiments were performed at two different incubation times: a short period of 2 h and a longer one of 24 h. The formation of AuNPs under these conditions was followed by confirmation with UV-vis spectroscopy and TEM.…”