Regular readers of this journal will have noticed that research papers reporting new or improved antimicrobial systems feature strongly in almost every issue. The number of pages devoted to the subject of antimicrobials reflects a real need to develop new ways of tackling an age-old problem. More recently, however, we have seen an upsurge in submissions on the application of nanotechnology in the battle against undesirable micro-organisms. The antimicrobial efficacy of many compounds can be enhanced by reducing their size to nanolevel, defined as having at least one dimension <100 nm. The enhancement is attributed to the higher surface-area-to-volume ratio which, in turn, leads to higher reactivity between antimicrobial agent and micro-organism.
In this virtual issue, nine papers on nano-antimicrobials, published in the 3-year period since January 2011, are presented. The issue begins with two reviews on the antimicrobial properties of sulphur and silver nanoparticles. These are followed by three original articles on silver nanoparticles and their action against yeast and bacteria. Notably, the two papers on the antimicrobial efficacy of silver nanoparticles against Candida biofilms offer contradictory conclusions regarding efficacy. A third paper on the growth dynamics of the Gram-negative soil bacterium Cupriavidus necator suggests that silver nanoparticles may, under certain circumstances, stimulate rather than inhibit bacterial growth. This suggests that the mode of action of silver nanoparticles needs to be further investigated in order to utilize these novel materials in a more predictable fashion.
Two papers focus on the antimicrobial properties of zinc nanoparticles. In the first of these, zinc oxide nanoparticles are shown to inactivate Campylobacter jejuni biofilms by penetrating through the extracellular matrix, entering the sessile cells and interacting directly with the quinone structures in nucleic acids. The second paper reports the results of Salmonella survival experiments in liquid egg albumen stored in bottles coated with zinc oxide nanoparticles combined with a range of natural antimicrobials including allyl isothiocyanate and nisin. The single-element theme continues with a paper on copper. In this article, the surface biocidal activity of copper alloys against Escherichia coli and Staphylococcus epidermidis was enhanced by the creation of organic copper nanoflowers on metal surfaces.
And finally, the virtual issue concludes with a paper suggesting that it may be possible to enhance the antifungal activity of chitosan by incorporating it in a nanoemulsion prior to coating tropical fruits intended for cold storage.