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 living cells, algae, molds, spores, fungi, viruses,
prokaryotic and eukaryotic microorganisms, even in relatively low
concentrations. This antimicrobial effect is shown by ions of mercury, silver,
copper, iron, lead, zinc, bismuth, gold, aluminium, and other metals.
Silver spoons self-sanitize due to the oligodynamic effect.
Mechanism
Several metal ions, especially heavy metals, show this
effect to various degrees. The exact mechanism of action is still unknown.
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 considered to be metabolically active outside
their host range.
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. 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.
Silver is capable of rendering stored drinking water potable
for several months. For this reason, water tanks on ships and airplanes are
often "silvered". Silver compounds such as silver sulfadiazine are
used externally in wound and burn treatments. 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. Silver-coated medical implants and devices have been
shown to be more resistant to biofilm formation. 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.
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.
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