Atomic force microscopy investigation of the characteristic effects of silver ions on Escherichia coli and Staphylococcus epidermidis

The influence of silver ions on Escherichia coli and Staphylococcus epidermidis has been investigated by atomic force microscopy (AFM). Both single cell and cell communities were visualized, and the nanoscale ultrastructure images of these two bacteria strains before and after stimulation of silver ions were obtained. The results showed that in the case of E. coli after treatment with silver ions, vesicles appeared on the cell walls, and the size of vesicles became larger with the increase of the incubation time. However, in the case of S. epidermidis after treatment with silver ions, irregular and deep grooves appeared on the cell walls, and the cytoplasm membrane shrank and became separated from the cell wall. The significant differences in cell wall changes between E. coli and S. epidermidis after treatment with silver ions were related to their structural characters. According to those results, it is shown that AFM can provide new insight into the antimicrobial mechanism of silver ions, and show a new methodological approach to understand the relationship between structure and function of microbial cell when it was exposed to external stimulation.