Mechanism of Action: How Colloidal Silver Does What It Does
The way colloidal silver works as an antimicrobial is an emerging knowledge field. Advances in equipment and methodology have enabled researchers to expand their understanding in this area. The current picture may seem complicated to individuals outside the spectrum of the medical field, but herein, we will attempt to present a simplified, relatively non-medical version of the colloidal silver mechanism of action as we currently know it.
There are several theories out there, and the most reliable, scientific one is based on the fact that silver ions kill bacteria through chemical reactions in several ways. One way is by attaching to key components of the cell membrane or other essential components of the cellular or viral structures; this attachment disables their normal function. Another valid theory is that silver ions combine and then recombine in a chain reaction with several chemical components that are vital for the microorganism.
Silver ions can interfere with cellular enzymes by binding to their amino acids, thus forming silver-amino acid complexes. When enzymes are blocked, so is their respiratory cycle, and free radicals form, promoting further damage to bacterial cells.
The biocidal effect of silver seems to be related to a mechanism involving the binding of silver to various amino acids, mainly those in the thiol (sulfur) groups, including the respiratory chain and citric acid cycle enzymes. This leads to their inactivation and bacterial death. Another mechanism of silver activity in bacteria is the formation of hydroxyl radicals, which leads to DNA damage.
Simply put, silver ions kill bacteria. The surface area plays a role in solid applications, but it has nothing to do with antibacterial properties. What is less understood by most is that if we place any solid substance in any liquid, a small quantity of that solid will be dissolved, and some will become ions. The number of ions may be extremely low, but in the case of silver, even that low concentration is millions of times higher than necessary for antibacterial applications.
Any competent high school chemistry student knows that a salt or chemical complex dissociates in water or liquid solution. The solubility product constant (Ksp) is universal.
The consequences are multiple. For one thing, silver ions attach to chloride, which may be considered insoluble, though nothing exists that is not at all soluble; Solubility may be high or low but not zero. This universal constant assures us that some of those silver chloride ions re-dissociate and form complex chloride ions that are soluble. Whatever other complex ions are produced later (with phosphates, sulfates, or amino acids, for example), at least part will further dissociate. This chemical chain reaction may play a great role in the killing of bacteria.
The following is an excerpt from Environmental Health Perspective, a journal by the National Institutes of Health:
“Silver nanoparticles are an effective tool for killing disease-causing bacteria. But despite their widespread use in catheters, clothing, toys, cosmetics, and many other products, investigators haven’t fully understood whether their effectiveness is a function of the release of germicidal silver ions, some feature specific to their nanoparticle form, or both. Researchers at Rice University now report evidence that the release of dissolved silver ions is the driving force behind silver nanoparticles’ germicidal action.
Silver ions are powerful antimicrobials, but they are easily sequestered by chloride, phosphate, proteins, and other cellular components.3 ”Silver nanoparticles are less susceptible to being intercepted and a more effective delivery mechanism,” says Pedro JJ Alvarez, Chairman of Rice’s Civil and Environmental Engineering Department. The nanoparticle form is therefore used to ferry silver ions to bacteria they could not reach on their own, for example, by coating devices such as catheters.”
The same conclusion has been drawn by other researchers. Jung et al. report, “Nanoparticles [ajc1] are effective at delivering silver ions…but their nano nature does not appear to imbue them with additional antimicrobial properties.”
However, one can not exclude that the surface charge may not be responsible for some unknown interactions with bacteria. It will likely bring the bacteria within proximity of the nanoparticle surface, where the concentration of silver ions is higher.
It is widely accepted that silver ion release is an important mechanism in terms of AgNP toxicity. Other described mechanisms have not yet been convincingly proven. Among them are contact toxicity due to electrical or other attraction forces that create interactions between the silver nanoparticles and bacteria. The formation of free radicals or reactive oxygen species (ROS) has been proposed; however, is this ROS formation a cause or a consequence of the enzymatic blockage by silver?
Silver-Colloids.com contains a collection of public, scientific information about colloidal silver. One of the articles on this site discusses how colloidal silver is produced. A circuit is made between a silver electrode and de-ionized water, which has no positive or negative electrical charge. An electric current is passed through this circuit, and that electricity causes silver nanoparticles and positive silver ions to detach from the silver electrode and move into the water. When the electric current is turned off, these particles and ions remain in the water.
As mentioned previously, silver content of colloidal silver is measured in parts per million (ppm). This figure describes the total concentration of silver in the liquid, the concentration of silver particles and positive silver ions. Generally, the total silver in these products is composed of 75 to 99 percent positive silver ions and the remainder of silver particles.
Research indicates that the silver ions are effective against microbes. When a person drinks colloidal silver, the silver ions move throughout the body and bind (attach) to parts of molecules, thiol groups. One place thiol groups are found is in the amino acid cysteine. Amino acids are the building blocks of genetic materials, DNA and RNA. They are also part of cofactors, helper molecules that assist the body in a variety of life-sustaining chemical reactions. Another group that utilizes thiol groups is enzymes, which can be thought of as the go-to guys that get things moving in the biological world. Enzymes catalyze (cause or increase the rate of) biochemical reactions, and without them, very little would happen within us.
As mentioned previously, it has been suggested that AgNPs may act as Trojan horses by entering the cells and then releasing silver ions that damage intracellular functions, but ions can damage the membrane too.
Silver attaches to the thiol groups that are essential for the wellbeing and survival of bacteria. Silver blocks the thiol groups from being able to participate further in chemical reactions, thus blocking the activity of many enzymes that are essential for bacterial survival. In many cases, silver interferes with bacteriological chemical reactions, preventing them from happening. In other instances, they change components of bacteriological substances, rendering them faulty or unstable. To date, much of the evidence supports the idea that the silver ion somehow enters the bacterial cell to disrupt their structure and their metabolism and finally kill them. A recent Italian study suggests that silver ions interact with proteins on the bacterial cell wall. This interaction creates cell membrane holes, enabling the cell cytoplasm (essential fluid inside the cell) to leak out. Ultimately, this results in cell death. In any event, whatever the mechanism of action, the end result is damage to microbes.
The therapeutic and toxic effects of silver can only be exhibited by free silver ions. Nevertheless, the threshold toxic values of silver must be interpreted with some caution, because the measured silver concentration may include both bound and free silver ions or nanoparticles.
Although the antimicrobial activity of silver is well known, little is known about the eukaryote detoxiﬁcation mechanisms. The question is often raised: Why does silver not have similar cytotoxic effects on eukaryotic cells as compared to bacterial cells? Eukaryotic cells are usually larger, with a higher structural and functional redundancy as compared to prokaryotic cells; therefore, higher silver ion concentrations are required to achieve comparable toxic effects to those on bacterial cells. This difference provides a therapeutic window in which bacterial cells are successfully attacked.
Colloidal Silver Conclusion 8: Positively charged silver ions, slowly released from particles of a professionally made colloidal silver solution, can enter the body. Once inside, these ions are somehow able to interfere with the normal workings of microbes, bringing about their destruction.
 “The Solubility Product Constant Ksp.” http://www.horton.ednet.ns.ca/staff/richards/apchemistry/apnotes/apeqkspnotes.pdf
 Key, Frances S. and George Maass. “Ions, Atoms, and Charged Particles.” http://www.silver-colloids.com/Papers/IonsAtoms&ChargedParticles.PDF
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