Mechanism underlying prolonged antibacterial effect of silver ion

Drug resistance mainly caused by the abuse of antibiotics is becoming more and more serious, therefore there is an urgent need to develop novel antibacterial agents. Due to its safety, non-resistance, and high stability, the antibacterial activity of silver ion (Ag⁺) has attracted the attention of more and more researchers. In order to explore the antibacterial mechanism of Ag⁺, several common aquatic bacteria (Escherichia coli, Aeromonas hydrophila, Streptococcus agalactiae, Bacillus subtilis, Edwardsiella ictaluri), were used to test the Ag⁺ tolerance or bactericidal activity and its "zombie effect" (the bacteria killed by Ag⁺ can kill other fresh bacteria). The results of tolerance experiments of bacteria to Ag⁺ showed that Ag⁺ had significant growth inhibition on all the five bacteria. The higher concentration of Ag⁺, the more apparent "zombie effect" was observed in the same species of bacteria as well as different species of bacteria. To further investigate the mechanism underlying the antibacterial activity of Ag⁺, the Ag⁺ treated A. hydrophila and S. agalactiae were observed by transmission electron microscopy (TEM). The TEM results demonstrated that Ag⁺ could cause the separation of the cytoplasmic membrane (CM) from the cell wall and discharge of cytoplasmic organelles, so it could cause the lysis of the bacterial cell wall. In summary, this study reveals the prolonged antibacterial mechanism of Ag⁺, which will pave a new way for the development of novel antibacterial agents.