MARIO PAGLIARO
Istituto per lo Studio dei Materiali Nanostrutturati, CNR, Palermo, Italy

The antibacterial activity of silver to preserve food and water quality and to heal wounds has been exploited by man since early civilizations, more than 6,000 years ago (1). Before the introduction of antibiotics in the 1940s, silver was the main antimicrobial agent available (1).

Since the early 2000s, the interest in silver as antimicrobial agent against bacteria and fungi has flourished again due the fact that silver ions (Ag⁺) are able to target almost all biomolecules in the bacterial cell at the same time thereby preventing mutant strains development, the resistance mechanism observed with antibiotics (2).

Carried by porin proteins, Ag⁺ and Ag nanoparticles (NPs) enter the cell membrane (3) causing its rupture and cytoplasmic leakage, driving the formation of highly oxidizing species including H₂O₂, and hydroxyl and superoxide free radicals which rapidly oxidise DNA, RNA and proteins (3). Most importantly from the viewpoint of practical application, the Ag⁺ ions are not deactivated by the killing mechanism, with the dead bacteria serving as a reservoir for releasing lethal ...