A mechanistic study of the antibacterial effect of silver ions onEscherichia coli andStaphylococcus aureus

TLDR

The study investigates how silver ions inhibit the growth of Escherichia coli and Staphylococcus aureus. Bacteria were treated with AgNO₃ and examined by electron microscopy and X‑ray microanalysis to assess morphological and elemental changes. Silver ion exposure caused membrane detachment, DNA condensation, and silver–sulfur granule formation that impaired DNA replication and protein activity, with Staphylococcus aureus exhibiting milder morphological alterations than Escherichia coli. © 2000 John Wiley & Sons, Inc., J Biomed Mater Res 52:662–668.

Abstract

To investigate the mechanism of inhibition of silver ions on microorganisms, two strains of bacteria, namely Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus), were treated with AgNO3 and studied using combined electron microscopy and X-ray microanalysis. Similar morphological changes occurred in both E. coli 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 E. coli recommended a defense system of S. aureus against the inhibitory effects of Ag+ ions. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 52, 662–668, 2000.