A mechanistic study of the antibacterial effect of silver ions on Escherichia coli and Staphylococcus aureus

摘要

To investigate the mechanism of inhibition of silver ions on microorganisms, two strains of bacteria, namely Cram-negative Escherichia coil (F. coil) and Gram-positive Staphylococcus aureus (S. aureus), were treated with AgNO_3 and studied using combined electron microscopy and X-ray microanalysis. Similar morphological changes occurred in both F. coil and S. aureus cells after Ag~+ treatment. The cytoplasm membrane detached from the cell wall. A remarkable electron-light region appeared in the center of the cells, which contained condensed deoxyribonucleic acid (DNA) molecules. There are many small electron-dense granules either surrounding the cell wall or depositing inside the cells. The existence of elements of silver and sulfur in the electron-dense granules and cytoplasm detected by X-ray microanalysis suggested the antibacterial mechanism of silver: DNA lost its replication ability and the protein became inactivated after Ag~+ treatment. The slighter morphological changes of S. aureus compared with F. coil recommended a defense system of S. aureus against the inhibitory effects of Ag~+ ions.