How Silver kills bacteria finally revealed

Filed 20 June 2013, 12:34 IST. Every price, volume and forecast below is reproduced as published on that date and is not a current quotation. For how the benchmarks themselves are set, see how gold is priced.

Silver's antibacterial effect had been used for millennia and explained by nobody. Research reported here identified the mechanism: silver ions interfere with bacterial iron metabolism and respiration, generate reactive oxygen species inside the cell, and increase the permeability of the cell membrane. The third effect is the practically important one: a more permeable membrane admits substances the bacterium would otherwise keep out, including antibiotics it had become resistant to.

That combination is why the finding mattered beyond wound care. Silver was not merely another antibacterial agent; it was a way of making existing antibiotics work again against organisms that had learned to survive them.

The mechanism, in order

Silver ions in solution bind readily to sulphur-containing groups in proteins, which is where the selectivity comes from: bacterial enzymes involved in respiration and in iron handling are rich in exactly those groups. Disrupting iron metabolism releases reactive oxygen species, which damage the cell from inside. Separately, the ions destabilise the membrane, so the cell leaks and admits material it should exclude.

None of these is a single lethal blow, and that is the point. An antibiotic typically attacks one target, so a single mutation can defeat it. Silver attacks several unrelated systems at once, which makes resistance a much harder evolutionary problem, the reason silver dressings have remained effective in clinical use for decades without the resistance collapse that followed most antibiotic classes.

Where it is actually used

Wound dressings for burns and chronic ulcers, coatings on catheters and other indwelling devices where biofilm formation is the main failure mode, water treatment, and antimicrobial surfaces. In each case the silver is delivered as ions released slowly from a carrier rather than as metal, because it is the ion and not the metal that does the work.

The limits are equally established. Silver is not a systemic antibiotic: it is topical, and ingesting colloidal silver has no demonstrated therapeutic benefit while carrying real risks including argyria, a permanent discolouration of the skin. The distinction between a validated topical application and an unvalidated oral one is the one this dispatch is most often read in search of, and it is worth stating plainly.

Why this is the archive's most durable page

Because the question does not expire. This dispatch held first place for "how does silver kill bacteria" and for "silver kills bacteria", and second for "does silver kill germs", for years after the publication closed. A mechanism is still the same mechanism a decade later, whereas a 2013 price forecast is only of historical interest. The editorial section collects the handful of pieces in this archive with that property.