Determination the Effect of Silver Nanoparticles on Gram-Positive Bacterial Cells by Atomic Force Microscopy

Abstract

The atomic force microscope (AFM) was employed to study the significant effects of silver (Ag) nanoparticles-treated on the elastic cell wall of bacteria. In this study, the exposed Staphylococcus aureus was grown at 37 °C for 14 h. The cultures were centrifuged and cell pellets were resuspended in Milli-Q water to prepare final bacterial suspensions. A drop of bacterial suspension was deposited on polydimethylsiloxane (PDMS) sheet and allowed to air dry at room temperature before imaging. The cell suspension was collected at certain time intervals from the beginning of the test. The morphology of the cell surface compares between without treatment and Ag-treated cell suspension was investigated. The force mappings were obtained for the PDMS substrate and for the bacteria while scanning obliquely. The contribution of the internal osmotic pressure, to obtain a quantitative measure for the elasticity of the cell wall, had to be estimated. The pyramid-shaped AFM tip indented into a soft cell and the resulting bacterial surface was flat, and irreversible changed of bacterial cell structure. The investigation is attempted to understand pronounced effect of Ag nanoparticles on the individual gram-positive bacterial cell after treated with Ag nanoparticles.