The bactericidal mechanism of action against Staphylococcus aureus for AgO nanoparticles

- S. aureus in water was more sensitive to AgO than in PBS, since AgO reacted with PBS and formed Ag3PO4.
- After killing S. aureus in water, AgO did not changed.
- AgO particles attached to cell surface then interacted with the cells, resulting in the increase of released silver contents.
- Cell membrane damages by AgO nanoparticles were supported by the leakages of K+, proteins and DNA.
- Serious cell morphological and structural changes were caused by AgO nanoparticles.

To identify the mechanistic effects of AgO nanoparticles on Gram-positive bacteria, S. aureus cells suspended in phosphate buffer solution (PBS) and deionized water were separately treated using AgO nanoparticles at different concentrations. The phase composition changes of the bactericide after killing S. aureus and the cellular responses of S. aureus to AgO were characterized by X-ray diffraction, atomic absorption spectrophotometer, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. The results show that AgO nanoparticles could kill S. aureus suspended in PBS and deionized water. The bactericidal effect of AgO bactericide against S. aureus in water was better than that in PBS, due to the formation of Ag3PO4 from the reaction between AgO and PBS. AgO nanoparticles exerted their bactericidal activity by multiple processes. AgO nanoparticles adhered to the surface of S. aureus cells firstly, then induced physical alterations in cell morphology and released silver ions, leading to initial injuries of cell membrane. Once membrane damage occurred, they entered the cells, and damaged the intracellular materials, eventually causing severe morphological and structural injuries to the cells and leakage of cytoplasm.