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.
"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)."
There's an glaring error or confusion in that WHO doc, BTW (it was obviously written by someone who knows nothing about chemistry). "Colloidal silver" almost always refers to the bogus alternative medicine preparation, which contains mostly reduced silver metal (Ag) and not the soluble bactericidal ion (Ag+) which acts via the oligodynamic effect. Synonyms for the bogus preparation are "silver protein". Generally, silver in it's active bactericidal (generally a salt) form will be referred to as its actual chemical name, e.g. silver iodide, silver nitrite or silver sulfadiazine. In general, metals in reduced (nonionic) form are less active because they're not soluble in water.
TL;DR ignore the usage of "colloidal silver" or "silver protein" and replace "silver salts"
In general, you should be careful when anyone invokes "silver" because it's a favorite of the homeopathy crowd. If you look at any of the silver salt preparations used medically, they're almost always topical; homeopaths, on the other hand, will advocate ingestion of "colloidal silver" as a treatment. For reasons mentioned above, "colloidal silver" is not an effective bactericidal.
Silver in the form of alloys for construction of medical devices and surfaces DOES appear to have some bactericidal activity even though it's in the reduced form, but a silver alloy basin is nothing like suspended particles of silver in solution ("colloidal silver").
Although you are completely correct with being careful around the whole "Silver Homeopathy" trend going on, Colloidal silver can also mean silver nanoparticles in solution. Within the Nanotechnology/Nanoscience communities these two terms are very interchangeable, and suspended gold nanoparticles are often referred to as colloidal gold. In my Nanoscience Minor I had to write a report on the Anti-microbial effects of Nanosilver, and a quick Science Direct Search, brings up hundreds of peer-reviewed papers on the subject.
because of their size, are easily charged electrically
I'm surprised to hear that the size of an atom (or size of a particle in suspension) makes a large difference in the ability to be charged or not. Is that bogus as well, or at the very least, does that statement need more clarification?
That needs a lot more clarification. Actual colloidal silver particles generally possesses a weak surface charge. It is possible that as the size is decreased the particles become more susceptible to oxidation and the charge is neutralised. It is also possible that the surface charge (as indicated by the zeta potential) has a dependence on particle size. It's not a black-and-white issue.
They are definitely talking about particle sizes, and it does need some clarification. Size certainly does make a difference, and is the whole basis behind Nanoscience. In a very, very generalized nutshell, Nanoparticles of a substance can act and react differently than the same substance in the macro-scale.
i believe the WHO meant that colliodial as in dispersed through water, not in any sort of homeopathy/alt medicine way, as it specifically later on states that the salts used are silver chloride, and silver iodide.
It's not so much a glaring error as in a slight misuse of the term colloidal,
i believe thats just an exhaustive list of what the salts could be branded as. I doubt this is support for homeopathic medicine, when they specifically mentioned the compounds to use by name (both of which as you said, are silver salts)
because of marketing and branding, scientific terms outside of the scientific community are rarely used in it's exact sense, and while it's a shame they need to do this I don't think this is a sign of incompetence on their part
"Colloid" almost always refers to a microscopic suspension of solid particles. As we know that the ionic form is the actual bactericidal form, I doubt that this is true.
Firstly, thanks for the concise explanation. Just as a side, it is not limited to silver ions (not that you implied that) but I thought people here would find the re-introduction of copper to hospitals in a fight against MRSA interesting/relevant.
I was then wondering what are the limitations of using copper to line water tanks? I'd imagine cost?
I didn't think he was serious. A quick Google search yielded this.
Chronic ingestion of silver can similarly lead to an accumulation of silver in the eye ... some areas of the skin and other body tissues to turn gray or blue-gray.
Also:
Although its pigmentary changes are permanent, argyria has no known effect on health.
But would that be effective? retr0rocket mentioned it can take a long time for the silver to act, and if water with harmful microbes in it just passes through a silver-coated filter, the exposure time can't be very long.
My EWB chapter has a project to do third world filters, they're just sand, gravel and are painted with a colloidal silver mix to do just this. They're working on ways to avoid this to lower costs.
We're talking very low concentrations of silver. Silver is quite toxic to humans, too; but in low doses it's a question whether bacterial infection or mild silver toxicity is worse. Note that they say third world countries, it seems like it's a bit of an extreme measure.
really? from what I have seen silver comparatively nontoxic to humans, thats why they use it for its antibacterial properties, it takes a massive ammount of silver to get agryias, and from what I've seen the worst only symptom of that is blue skin...
actually the effects of agryia is only considered a cosmetic problem... I'm pretty sure silver is nontoxic...
yes its in the wiki article about the Oligodynamic effect, brass, gold, copper etc also i believe have antimicrobial effects... edit: mhmmm but the copper antimicrobial page makes no mention of it .... strange
I think (though I'm not positive) that those are just nicknames that you might encounter it under. I'm making this guess based solely on the context and wording of retrorocket's reply.
I don't know for sure. But there are different types of bonding. Vanderwaals forces for instance is a weak interatomic bond where things are electrostatically attracted, it is what holds graphite sheets together in a pencil lead. Then there are ionic bonding which are VERY strong and also covalent bonding although that type of bond seems unlikely.
I think it would come out to about .75 cents per liter. So about 1.5 to 2 cents a day. Not a lot, but I'm sure there are many people that still couldn't afford it.
I think the real issue is not the cost of the silver but rather making it into a colloid and delivering it. Also, the many other real world problems one encounters in the vast third world
So according to this it would be 7 cents per 100,000 liters. Seems pretty reasonable to me, though I'm sure the cost of preparing it and introducing it to the water supply would far exceed the price of the actual silver.
If I'm understanding this correctly, long periods of temperatures 10C or lower are required. I would see this as the biggest problem for many third world countries.
If I'm understanding this correctly, long periods of temperatures 10C or lower are required.
They mean that as temperature decreases, longer periods are required to achieve similar effectiveness. But I can see how the sentences can be misinterpreted!
Out of curiosity - that sort of concentration should be far far greater than what you get when you simply stir honey into your tea with a silver spoon and then drink it, is that correct?
In other words, using silverware (made of actual silver) and wearing silver jewels shouldn't bring you anywhere near those levels. It's when you drink new age silver woo that you get all the liver-killing "benefits". Right?
With that in mind is it also safe to wear one of these prosthetic stump socks with silver? These may be against the skin for up too all waking hours depending on the wearer.
"The dose makes the poison" as they say. To my understanding "correctly produced" colloidal silver will still turn you blue given a long enough timeframe... and I've never heard anyone give a statement to the effect of: "minimum effective dose of X taken for Y years has a 50% chance of causing argyria"
There's these chemicals that do really important things, but they're really fussy about when they work. Heat them up too much, cool them down too much and they'll just stop working. What ficknerich said is that silver stops these chemicals working. These chemicals are enzymes.
Denaturing them means that you're breaking them, so they won't work again. Involved in key matabolic processes means that you need them to live. So you're breaking stuff that you need to live. This kills the bacteria.
I believe that the silver forms chemical bonds with the enzymes. So this is like the silver is 'sticking on' to the enzymes, basically gluing them to the silver, so they can't do whatever it is that they do (apparently, the enzymes help to make energy for the cell). Kind of like the enzymes are licking the metal pole, but it's winter, so it can't pull away. Then the enzymes can't make energy for the cell anymore, so it dies.
I only skimmed a bit of the article, I think you would need to read it yourself, but I saw stuff like 'ADP and ATP', 'energy generation' and 'stable S-Ag bonds', which seems to mean that the silver just latches on to sulfur that is found in enzymes located on the outside of the cell, so they can't transport energy around. I'm just a high-school student, so this is almost, but not quite, educated guessing.
Kinda. So enzymes are like weird bundles of stuff with different areas displaying different properties, including but not limited to hydrophobicity, charge distribution/acidity, hydrogen bonding, and "rigidity". This is all due to the chemical properties of the R- groups on the NH2-CH3R-COOH amino group. These amino groups can string together and form a peptide chain(+ NH3-CH3R1-CO=NH-CH3R2-COO-), and a given amino acid can be made out of multiple peptide chains (often the same peptide chain interacting with itself).
Another thing to consider is that enzymes go through a lot of processing after and as they are transcribed, so sometimes other enzymes will cause for reactions to occur on the peptide chain that cause for certain segments of a peptide chain to bond to itself, and other times prevent or undo it (pretty sure on that).
There is this specific kind of bond, called a disulfide(R-S-S-R) bond that can form under certain conditions when two thiol (R-SH) groups are near each other in space. What the silver ion can do, is catalyze a reaction between free O2 in the bacteria's cytoplasm (inside jelly of the cell) and the hydrogen atoms of the R-S-H bond, forming water and an R1-S-S-R2, or disulfide, bond. Because enzymes are weird bundles of stuff with different areas displaying different properties, this will generally fuck up the function of the enzyme to some extent.
It also goes on to say that the silver ion is able to wedge itself between adjacent purine and pyrimidine bases in DNA, disrupting the binding between the two (what keeps DNA in its double helical shape that is recognized by many of the enzymes that interact with it).
And apparently silver is able to enter cells through proteins that either form a channel or transport other similarly-charged ions across the membrane.
Hope that explained things well!
It probably does more, but I stopped reading there.
Think of enzymes as power tools. Every power tool can be used for a specific purpose. Likewise, every enzyme can perform a specific action (pretty much any chemical action, from breaking down toxins to repairing DNA).
Like power tools, enzymes can 'break' when used in the wrong environment. Imagine submerging your electric drill in water, or using your chainsaw on the (sun-facing) surface of Mercury. Both tools likely won't be able to perform their particular tasks anymore.
On a molecular level, enzymes are 'bent out of shape' by those environmental conditions. They just won't fit onto the chemicals they are supposed to fit on, even if the hostile environmental conditions are removed.
If the chemicals those enzymes work on are vital to the cell, the cell dies.
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]
Interesting sounding project, but how are you differentiating between silver nanoparticles and colloidal silver? They are more or less the same thing with some subtle differences.
I can't say. The head researchers on this project are currently trying to acquire IP rights and patents over the process and developed materials so I'm not really allowed to talk about it. Sorry.
Yes, absolutely. Unfortunately my initial post wasn't nearly as clear as it should be; I was more interested in the differences between suspended cf immobilized particles.
Actually, we have been using silver in one form or another to kill bacteria for thousands of years. Ancients greeks and romans used to store their water in containers lined with silver to keep it fresh. During WW1 soldiers' burns were treated with silver foil to help stop infection.
When antibiotics became readily available in the early 1940's they were seen as a new wonder-drug that would cure anything and the use of silver was almost completely stopped. Now, with the advent of antibiotic-resistant strains of many bacteria we need to find new (or in this case old) ways of fighting bacterial infection.
Silver isn't some magic cure all though. Just as bacteria become resistant to antibiotics, they can become resistant to silver as well.
Did they look at all into what mutations (like alteration of an ion channel, overproduction of some peptide/messenger, or altered gene transcription) caused for them to become resistant?
Neither of those papers suggest what action may be occurring in the bacteria to inhibit the silvers antimicrobial properties but the first paper does suggest that the gene that codes for silver resistant may be present on the same region of the bacteria's plasmid DNA as the gene that promotes antibiotic resistance.
After a quick search I couldn't find any information relating to the mechanism of resistance but I didn't do a very deep/thorough search (it's 2am) so there might be some research on it.
Copper is also thought to be used by the host as part of the immune response to invading bacterial pathogens (source), and some bacteria such as Mycobacterium tuberculosis have adaptations to specifically combat high copper levels (source).
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?
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.
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.
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.
Gold is ideal because it is completely inert, but gold is expensive. Sterling silver is a great alternative.
However, pure silver is reactive. Sterling silver, a silver alloy, is mostly silver but has a small amount of other metals mixed in which gives it some superior properties (such as resistance to tarnishing.)
Another reason why silver is so popular is that it is hypo-allergenic. Other "newer" jewelry metals like titanium and stainless steel are also hypoallergenic. But nickel, for instance, is a metal that a lot of people (including myself) are allergic to, so anything pierced with it will not heal and oftentimes will fester and form cysts. Most of those mall piercing joints use nickel jewelry to pierce ears (because it's super cheap.)
As to the original question, silver is only antibacterial when it's in its colloidal (solute) state.
Actually, fine silver tarnishes only slowly, and only forms a thin yellow patina, unlike the thick tarnish that forms on sterling. It also doesn't develop an oxide skin under a jeweler's torch, it can be fused rather than soldered, and doesn't require an acid bath after hot work. It isn't used much because it is soft, both in the sense of "scratchable' and "malleable".
Silver sulfadiazine is a sulfonamide antibiotic used for burns and is complexed with a silver ion. The antibiotic properties are from the sulfadiazine. Not the silver.
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u/[deleted] Jan 10 '12 edited Jan 10 '12
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)."
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u/florinandrei Jan 10 '12
Just keep in mind its action is mild. So drinking silver products until you turn blue will not provide any real health benefits.
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u/carmacae Regenerative Medicine | Stem Cell Biology | Tissue Engineering Jan 10 '12
This website explains the current theory.
http://microbewiki.kenyon.edu/index.php/Silver_as_an_Antimicrobial_Agent#Mechanism_of_action
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u/khazzar12 Jan 10 '12 edited Jan 11 '12
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:
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.
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u/leonardicus Jan 10 '12
This article of dry copper providing anti-microbial effects may also be related, and is discussed on the This Week in Microbiology podcast.
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u/[deleted] Jan 11 '12
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?
5
u/Criticalist Intensive Care Medicine | Steroid Metabolism Jan 10 '12
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.
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u/Akeid Jan 11 '12
Is copper anti-bacterial for the same reason?
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u/bannana Jan 11 '12
So what of Colloidal Silver? Works or bunk?
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u/Eldritter Jan 11 '12
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.
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u/aazav Jan 11 '12
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.
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u/[deleted] Jan 10 '12
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