Eco-friendly synthesized spherical ZnO materials: Effect of the core-shell to solid morphology transition on antimicrobial activity.

ZnO materials with spherical morphology, core-shell and solid, disperse or interconnected, were obtained by a completely green synthesis via a carbohydrate-template route. Morphology, structure and optical properties, as well as antimicrobial potential and cytocompatibility were investigated. The antimicrobial efficiency of the obtained materials was screened against a large spectrum of reference and clinical microbial strains, both susceptible and exhibiting resistance phenotypes of clinical and epidemiological interest, in planktonic and biofilm state. Their biocidal activity is strongly dependent of material's characteristics and target microorganism. One of the most valuable findings of our study is the good antibiofilm activity of the obtained nanostructures, which in some cases was superior to that noted against planktonic cells, despite the well-known high tolerance of biofilm-embedded cells to different stressor agents. Another important finding is the excellent efficiency against three Gram-negative, respectively Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae and two Gram-positive species, i.e. Staphylococcus aureus and Enteroccus faecium included in the ESKAPE list of the most dangerous resistant pathogens, requiring global surveillance and urgent need for the development of novel antimicrobial agents. Our study offers the first insight regarding the high therapeutic potential of ZnO nanoparticles against the fearful nosocomial pathogen A. baumannii. The cytocompatibility of the developed materials in terms of cell morphology, viability and proliferation, revealed a comparable dose-dependent cellular response, at the active antimicrobial concentrations, only a low effect on cell viability is evidenced. Overall, our data demonstrated the potential of the materials for antimicrobial applications and also that their biotoxicity can be modulated directly through their morpho-structural characteristics.