Insights into the antibacterial properties of cancer theranostic zinc-dopped iron oxide ZnxFe3-XO4 nanoparticles

The global mortality rate from antimicrobial-resistant infections is steadily rising, driven primarily by the widespread use of antibiotics in the last decades, a problem exacerbated during the COVID-19 pandemic. The exponential growth of antimicrobial resistance far outpaces the current development of new antibiotics. One promising strategy to counteract the rise of antibiotic-resistant bacteria is the use of nanomaterials as antimicrobial agents. In recent works, Zinc-Doped Iron Oxide ZnxFe3–xO4 nanoparticles (NPs) have been demonstrated as a highly efficient cancer theranostics agent capable of several different, complementary, therapeutic routes, depending on the Zn doping concentration. In this study, we demonstrate for the first time the interesting antibacterial effects of this nanomaterial, investigating the interactions of ZnxFe3–xO4 NPs with various Zn concentrations (0.2 %, 1 %, 1.5 %, 2 %) with two opportunistic pathogens: the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Pseudomonas aeruginosa, both of which are among the top resistant nosocomial pathogens, and model organisms. We adopt a holistic approach, looking at: (i) the antimicrobial effects of ZnxFe3–xO4 NPs, either alone, or in combination with two antibiotics, gentamicin (CN) and ciprofloxacin (CIP), (ii) their efficacy at dispersing bacterial planktonic aggregates, and (iii) their inhibitory properties of biofilm formation. Last, we employ Atomic Force Microscopy (AFM) for qualitative and quantitative analyses of bacterial cells treated with CIP, CN, and ZnxFe3–xO4 NPs to enable knowledge of the mechanisms of antibacterial action of the latter.