Oligodynamic effect

Silver spoons self-sanitize due to the oligodynamic effect

The oligodynamic effect (Greek: oligos = few, Greek: dynamis = force) was discovered in 1893 by the Swiss Karl Wilhelm von Nägeli as a toxic effect of metal ions on viruses and living cells e.g. algae, moulds, spores, fungi, prokaryotic and eukaryotic microorganisms, even in relatively low concentrations.^[1] This antimicrobial effect is shown by ions of mercury, silver, copper, iron, lead, zinc, bismuth, gold, aluminium, and other metals.

Mechanism

Several metal ions, especially heavy metals, show this effect to various degrees. Bacteria are in general affected by the oligodynamic effect. Viruses in general are not very sensitive to this effect. This disparity suggests that the mechanisms exerting the most influence over toxicity are interfering with metabolism, since viruses are not metabolically active.

Data from silver suggest that these ions denature enzymes of the target cell or organism by binding to reactive groups, resulting in their precipitation and inactivation.^[2] Silver inactivates enzymes by reacting with the thiol groups to form silver sulfides. Silver also reacts with the amino-, carboxyl-, phosphate-, and imidazole-groups and diminish the activities of lactate dehydrogenase and glutathione peroxidase.

Applications

Certain metals, such as silver, copper and copper alloys, are known to be far more poisonous to bacteria than others, such as stainless steel and aluminium, which is why they are used in mineral sanitizers for swimming pools and spas.

Many infections can be spread by doorknobs. Brass doorknobs disinfect themselves in about eight hours, while stainless steel and aluminium knobs never do. Unvarnished brass doorknobs therefore tend to be more sanitary than stainless or aluminium doorknobs. The effect is important in hospitals, and useful in any building.^[3]

Silver is capable of rendering stored drinking water potable for several months. For this reason, water tanks on ships and airplanes are often "silvered".^[4] Silver compounds such as silver sulfadiazine are used externally in wound and burn treatments.^[5] Silver nanoparticles, obtained by irradiating a silver nitrate solution with an electron beam, are effective bactericides, destroying gram-negative species immune to conventional antibacterial agents.^[6] Silver-coated medical implants and devices have been shown to be more resistant to biofilm formation.^[7] Silver nitrate has been shown to be effective in inhibiting the development of the herpes simplex type 1 virus though it is largely ineffective against type 2.^[8]

Resistance

Metal ions (as does ultraviolet light) also cross react with antibiotics in selecting resistant strains of microbes leading to emergence of resistance transfer factors, genetic factors that can spread to other species in hospitals and on farms.^[9]

See also

• Medical uses of silver

References