Can disc diffusion susceptibility tests assess the antimicrobial activity of engineered nanoparticles?

Angeliki Kourmouli; Marco Valenti; Erwin van Rijn; Hubertus J E Beaumont; Olga-Ioanna Kalantzi; Andreas Schmidt-Ott; George Biskos

doi:10.1007/s11051-018-4152-3

Can disc diffusion susceptibility tests assess the antimicrobial activity of engineered nanoparticles?

J Nanopart Res. 2018;20(3):62. doi: 10.1007/s11051-018-4152-3. Epub 2018 Mar 2.

Authors

Angeliki Kourmouli^{1

2

3}, Marco Valenti¹, Erwin van Rijn⁴, Hubertus J E Beaumont⁴, Olga-Ioanna Kalantzi², Andreas Schmidt-Ott¹, George Biskos^{5

6}

Affiliations

¹ 1Faculty of Applied Sciences, Delft University of Technology, 2628-BL Delft, The Netherlands.
² 2Department of Environment, University of the Aegean, 81100 Mytilene, Greece.
³ 3Present Address: The Birmingham Institute of Forest Research (BIFoR), School of Geography Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT UK.
⁴ 4Kavli Institute of Nanoscience, Department of Bionanoscience, Delft University of Technology, 2628-CJ Delft, The Netherlands.
⁵ 5Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628-CN Delft, The Netherlands.
⁶ 6Energy, Environment and Water Research Center, The Cyprus Institute, 2121 Nicosia, Cyprus.

Abstract

The use of disc diffusion susceptibility tests to determine the antibacterial activity of engineered nanoparticles (ENPs) is questionable because their low diffusivity practically prevents them from penetrating through the culture media. In this study, we investigate the ability of such a test, namely the Kirby-Bauer disc diffusion test, to determine the antimicrobial activity of Au and Ag ENPs having diameters from 10 to 40 nm on Escherichia coli cultures. As anticipated, the tests did not show any antibacterial effects of Au nanoparticles (NPs) as a result of their negligible diffusivity through the culture media. Ag NPs on the other hand exhibited a strong antimicrobial activity that was independent of their size. Considering that Ag, in contrast to Au, dissolves upon oxidation and dilution in aqueous solutions, the apparent antibacterial behavior of Ag NPs is attributed to the ions they release. The Kirby-Bauer method, and other similar tests, can therefore be employed to probe the antimicrobial activity of ENPs related to their ability to release ions rather than to their unique size-dependent properties. Graphical abstractᅟ.

Keywords: Aerosol-based nanoparticle synthesis; Antimicrobial activity; Disc diffusion method; Engineered nanoparticles; Gold nanoparticles; Silver nanoparticles.