This article reports the excellent antimicrobial response of nanoparticulate ZnO against multidrug-resistant organisms (MDROs). We demonstrate that the enhanced antimicrobial activity against MDROs depends on the crystalline defects of ZnO. Hence, this work provides insights on the ZnO-microorganism interactions, and we pose combined physico-chemical action mechanisms against resistant bacteria. Highlights-Synthesis of ZnO nanoparticles with antimicrobial response against multidrug-resistant organisms.-A high crystal defect concentration leads to a high surface reactivity and they improve the antibacterial response -A combined action of surface reactivity is mandatory to obtain this inorganic antimicrobial agent.

The extensive range of applications where synthetic nanomaterials are nowadays used is causing a huge commercial market. An incipient use of these nanomaterials arises from the need to generate alternative antimicrobial agents, anticipating the development of resistant microorganisms. Here, we show a nanostructured ZnO with antimicrobial properties and low-cytotoxicity based on a nanoparticles arrangement by controlling the formation of sintering-neck into nanoporous spheres. The antimicrobial effectiveness of ZnO spheres is tested in a broad-spectrum of microorganisms such as fungi, Gram-negative and Gram-positive bacteria. The hierarchical structures show highly effective antimicrobial activity at low concentrations and in relatively short action times (24-72h). We demonstrate that the enhanced antimicrobial properties against microorganisms are ascribed to a combining of both physical and chemical interactions between microorganism and ZnO. The approximation mechanism between microorganism and ZnO is provided through electrostatic forces (physical interaction) which, thanks to the ZnO-microorganism proximity, promote a rapid release of zinc cations and the reactive oxygen species penetration into microorganisms (chemical interaction). We believe that this work provides insights on the mechanisms underlying the interactions ZnOmicroorganism and possess a combined action mechanism for which nanostructured ZnO is so effective to combat microorganisms.

No abstract

The increasing threat of multidrug-resistance organisms is a cause for worldwide concern. Progressively microorganisms become resistant to commonly used antibiotics, which are a healthcare challenge. Thus, the discovery of new antimicrobial agents or new mechanisms different from those used is necessary. Here, we report an effective and selective antimicrobial activity of microstructured ZnO (Ms-ZnO) agent through the design of a novel star-shaped morphology, resulting in modulation of surface charge orientation. Specifically, we find that Ms-ZnO particles are composed of platelet stacked structure, which generates multiple Schottky barriers due to the misalignment of crystallographic orientations. We also demonstrated that this effect allows negative charge accumulation in localized regions of the structure to act as "charged domain walls", thereby improving the antimicrobial effectiveness by electric discharging effect. We use a combination of field emission scanning electron microscopy (FE-SEM), SEM-cathodoluminescence imaging, and Kelvin probe force microscopy (KPFM) to determine that the antimicrobial activity is a result of microbial membrane physical damage caused by direct contact with the Ms-ZnO agent. It is important to point out that Ms-ZnO does not use the photocatalysis or the Zn released as the main antimicrobial mechanism, so consequently this material would show low toxicity and robust stability. This approach opens new possibilities to understand both the physical interactions role as main antimicrobial mechanisms and insight into the coupled role of hierarchical morphologies and surface functionality on the antimicrobial activity.