Zinc oxide nanoparticles (ZnO NPs) are one of the most widely used nanoparticulate materials due to their antimicrobial properties, but their main mechanism of action (MOA) has not been fully elucidated. This study characterized ZnO NPs by using X-ray diffraction, FT-IR spectroscopy and scanning electron microscopy. Antimicrobial activity of ZnO NPs against the clinically relevant bacteria Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and the Gram-positive model Bacillus subtilis was evaluated by performing resazurin microtiter assay (REMA) after exposure to the ZnO NPs at concentrations ranging from 0.2 to 1.4 mM. Sensitivity was observed at 0.6 mM for the Gram-negative and 1.0 mM for the Gram-positive cells. Fluorescence microscopy was used to examine the interference of ZnO NPs on the membrane and the cell division apparatus of B. subtilis (amy::pspac-ftsZ-gfpmut1) expressing FtsZ-GFP. The results showed that ZnO NPs did not interfere with the assembly of the divisional Z-ring. However, 70% of the cells exhibited damage in the cytoplasmic membrane after 15 min of exposure to the ZnO NPs. Electrostatic forces, production of Zn2+ ions and the generation of reactive oxygen species were described as possible pathways of the bactericidal action of ZnO. Therefore, understanding the bactericidal MOA of ZnO NPs can potentially help in the construction of predictive models to fight bacterial resistance.

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Zinc oxide nanoparticles (ZnO NPs) are one of the most widely used nanoparticulate materials due to their antimicrobial properties, but their main mechanism of action (MOA) has not been fully elucidated. The study characterized ZnO NPs using X-ray diffraction, FT-IR spectroscopy and scanning electron microscopy. Antimicrobial activity of clinically bacteria Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa was evaluated by REMA after exposure to the ZnO NP at concentrations from 0.2 to 1.4 mM. Sensitivity was achieved at 0.6 mM for the Gram-negatives and 1.0 mM for Gram-positives cells. The effect of ZnO NPs on the membrane integrity and in the interference of cell division was investigated by its effect on the divisional ring, through fluorescence microscopy assays using B. subtilis (amy::pspac-ftsZ-gfpmut1) expressing FtsZ-GFP. Results showed that ZnO NPs did not interfere with the assembly of the divisional Z-ring. However, 70% of the cells showed damage in the cytoplasmic membrane after 15 min of exposure to the ZnO NPs. Electrostatic forces, production of Zn2+ ions, generation of reactive oxygen species were described as pathways of bactericidal action by ZnO. Thus, understanding bactericidal MOA can produce predictive models to prevent bacterial resistance and lead to further research.

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