Why is Silver Anti-Bacterial?

carmacae · 4 months

This website explains the current theory.

http://microbewiki.kenyon.edu/index.php/Silver_as_an_Antimicrobial_Agent#Mechanism_of_action

khazzar12 · 4 months

Finally an AskScience question I can be genuinely helpful in!

I'm currently working on this for my final year under graduate project and I recently completed a literature review on the antimicrobial properties of silver nanoparticles (very very small amounts of silver). While their antimicrobial action isn't exactly the same as colloidal silver or solid silver I think it's still relevant so I'll just copy+paste what I wrote about it:

There is still quite a lot of debate in the scientific community on the exact mechanism by which silver nanoparticles carry out their antimicrobial action. However, the main mechanism by which silver nanoparticles exhibit their antimicrobial action appears to be through the release of silver ions.[14] There has, however, been quite a lot of contradicting literature on the subject. It has also been suggested that the silver nanoparticles causes the formation of reactive oxygen species (ROS)[15] and that silver nanoparticles directly damage the bacterial cell membrane. In fig.1 below these three mechanisms are illustrated.

If the silver nanoparticles released silver ions, the ions may interact with membrane proteins and affect their function. The silver nanoparticles may also induce the formation of ROS which could cause the degradation of the bacterial cell’s DNA. The ROS could cause oxidative damage to the bacterial cell membrane as well as membrane proteins. The silver nanoparticles could also directly affect the membrane of the bacterial cell.[16]

Edit: Was asked to provide my citations:

[14] Feng, Q.L et al., 2000. A mechanistic study of the antibacterial effects of silver ions on Escherichia coli and Staphylococcus aures. Journal of Biomedical Materials Research, 52(4), 662-668. Additional Pubmed link.

[15] Jun, S.K et al., 2007. Antimicrobial effects of silver nanoparticles. Nanomedicine: Nanotechnology, Biology and Medicine, 3(1), 95-101.

[16] Marambio-Jones, C. et al., 2010. A review of the antibacterial effects of silver nanomaterials and potential implications for human health and the environment. Journal of Nanoparticle Research , 12(5), 1531-1551.

Sorry for using tinyurl links but the actual urls had internal parentheses that messed with the formatting.

retr0rocket · 4 months

i believe the antibacterial effects of silver and silver ions come from Oligodynamic effect (http://en.wikipedia.org/wiki/Oligodynamic_effect) which is like heavy metal poisoning for microbes. this effect in silver has been pretty well documented, they use silver to line the water tanks of ships and stuff to keep the water drinkable.

http://en.wikipedia.org/wiki/Medical_uses_of_silver

also the WHO recommends silver as one of the ways to disinfect water in third world countries, http://whqlibdoc.who.int/paho/2003/a85637.pdf (pg147)

"Silver has disinfecting properties only in its colloidal state —when it is in the form of extremely small particles in suspension which, because of their size, are easily charged electrically. In this state, it is also known as silver protein, silver salts, weak silver protein and strong silver protein. The salts that are used are silver chloride and silver iodide. In its colloidal form, silver does not eliminate viruses, but is considered highly effective in destroying different types of bacteria. Silver’s disinfection mechanism acts by inactivating bacteria and mold cell enzymes that need oxygen for their metabolism; its causes their cellular disruption, although over periods that vary widely according to the water temperature. Very long periods are required at temperatures of 10 °C or less, making it difficult to determine silver’s precise germicidal power. Colloidal silver can remain in the water for a long period of time, but is not considered to have good residual power because of the slowness of its reactions in eliminating organic matter. The recommended dose for high germicidal efficacy is in the range of 25 to 75 micrograms of silver per liter (0.025 – 0.075 mg/l)."

florinandrei · 4 months

Just keep in mind its action is mild. So drinking silver products until you turn blue will not provide any real health benefits.

leonardicus · 4 months

This article of dry copper providing anti-microbial effects may also be related, and is discussed on the This Week in Microbiology podcast.

smeezy · 4 months

Reading the responses, I find it hard to distinguish whether "solid" metal silver (as in, silver spoons, silver threads woven into "antibacterial" towels) is antibacterial, or only ionic silver, dissolved in a liquid. Can someone help me understand this better?

Criticalist · 4 months

We use this property of silver in some of our burns dressings in the ICU. Acticoat and SSD (Silver Sulphadiazene Cream) are both commonly used burns dressings. You do need to be careful as they often will cause the patients white blood cell count to transiently drop, which can worry you if don't realise what is doing it.

Akeid · 4 months

Is copper anti-bacterial for the same reason?

playerra · 4 months

Copper has the same anti-bacterial properties. This is the reason many door handles and railings around hospitals are coated with the element.

Trillian42 · 4 months

I have a related question. Is the fact that silver is anti-bacterial the reason why earrings are generally made out of sterling silver?

bannana · 4 months

So what of Colloidal Silver? Works or bunk?

pharmer2012 · 4 months

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Eldritter · 4 months

Silver nitrate (which has antibacterial properties) is dripped into the eyes of Newborn infants to prevent infections that can often get into infant eyes (from the vagina)... Silver nitrate is antibacterial because it has reactive chemical properies. Silver is not antibacterial as a metal (its also not soluble in solution). However, most of the time metals are bad for cell membrane stability so if a bacterium was on a silver ring and dried up there it would probably die.

aazav · 4 months

It's all about electrons. The free particles of silver are rather easily able to be charged or discharges, making them able to take an electron from something that might need it.

Copper and other metals (silver is too expensive) are often used in marine paint to prevent larval creatures from settling on the surface of ships and other submerged items.

4 months

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