Sweat disables copper’s antibacterial properties, with implications for doorknobs and handles everywhere. Bacteria, sweat, and copper. I’m Bob Hirshon and this is Science Update. Copper-containing metals like brass have antibacterial properties—a selling point for brass doorknobs, sink handles, and other fixtures in hospitals and schools. But now, British scientists have found that handling those fixtures can actually disable their germ-killing powers. According to University of Leicester forensic scientist John Bond, human sweat forms a corrosive layer on the metal surface. That blocks an exchange of charged particles that would otherwise kill harmful bacteria. And the fixtures that are handled the most would be the most affected. Bond:The more often it’s touched, you’re replenishing and indeed concentrating the active ingredient in sweat that corrodes the metal, which is just salt. So even if an institution has germ-resistant copper fixtures, they still need to clean them and encouraging frequent hand-washing.
I’m Bob Hirshon for AAAS, the Science Society. You may have heard that doorknobs and sink handles are big germ-carriers. With so many people handling them all day long, often one right after another, it isn't hard to see how germs from one person's hand could end up on another's by way of a doorknob. You probably didn't know that copper had antibacterial properties. But if it were your job to design the interiors of large buildings, or buy fixtures for schools, hospitals, or other big institutions, you'd probably have heard this. Manufacturers often promote copper's proven bacteria-killing properties to sell fixtures made of brass, bronze, or other metals with a high copper content. This experiment shows the importance of considering all factors before reaching a conclusion. Copper helps kill germs; therefore, it makes sense that copper-based doorknobs would pass along fewer germs than knobs made of glass, plastic, steel, or other materials. However, there's a crucial factor that may be left out of this scenario: the sweat from the hands that touch the doorknobs.
It was known that sweat can corrode copper alloys (metal mixtures) like brass in the long term. But in this study, the researchers studied the effects of sweat on copper surfaces within a few hours of contact. They found that within as little as an hour, the salt in sweat can form a corrosive layer on the surface of the metal, which would prevent the electrochemical reaction that kills microorganisms. Now, a full hour after someone touches a doorknob may sound like a long time for this effect to take hold. But consider how many people handle doorknobs or similar fixtures in a day: more than enough to neutralize the metal's germ-killing powers as long as the building stays busy. What's more, Bond points out that frequently touched items collect salts from the sweat of many people, which makes the corrosive layer tougher and longer lasting. It would be difficult to study this in a real-life setting, for a number of reasons. In order to control the study properly, researchers would have to study bacterial colonies on brass fixtures handled all day long, and compare them to other brass fixtures that were somehow protected from sweat but exposed to the same people's skin microorganisms.
However, the research suggests that institutions using copper-based fixtures shouldn't slack off on cleaning them, nor should they make any less of an effort to make sure people keep washing their hands. Now try and answer these questions: In the Science Update Triclosan and Staph, learn how some antibacterial chemicals may actually backfire and actively help a kind of bacteria they're designed to kill. The Science Update UV Disinfectant describes another approach to helping keep hospitals germ-free. For more about alloys, see the video Shape Memory Alloys, in which Dr. Ainissa Ramirez, associate professor of mechanical engineering and materials science at Yale, demonstrates "metals with a memory" used in space, in robots, and even in your mouth! In the Science Update lesson Triclosan and Staph, students can learn how some antibacterial chemicals may actually backfire and actively help a kind of bacteria they're designed to kill. The Science Update lesson UV Disinfectant describes another approach to helping keep hospitals germ-free.
For more about alloys, see the video Shape Memory Alloys, in which Dr. Ainissa Ramirez, associate professor of mechanical engineering and materials science at Yale, demonstrates "metals with a memory" used in space, in robots, and even in your mouth! Sleep & Gene Expression Silver spoons self-sanitize due to the oligodynamic effect The oligodynamic effect (from Greek oligos "few", and dynamis "force") is a biocidal effect of metals, especially heavy metals, even in low concentrations. The effect was discovered in 1893 by Karl Wilhelm von Nägeli, although he did not identify the cause.[1] Brass doorknobs and silverware both exhibit this effect. The metals react with thiol (SH) or amine (NH) groups of enzymes or proteins, a mode of action to which microorganisms may develop resistance. Such resistance may be transmitted by plasmids. Aluminium acetate (Burow's solution) is used as an astringent mild antiseptic.[3] Aluminium-based antiperspirant ingredients ("aluminum salts") such as aluminum chlorohydrate, activated aluminum chlorohydrates, and aluminum-zirconium-glycine (AZG) complexes work by forming superficial plugs in the sweat ducts, reducing the flow of perspiration.
Orthoesters of diarylstibinic acids are fungicides and bactericides, used in paints, plastics, and fibers.[5] Trivalent organic antimony was used in therapy for schistosomiasis. For many decades, arsenic was used medicinally to treat syphilis. It is still used in sheep dips, rat poisons, wood preservatives, weed killers, and other pesticides. Arsenic is also still used for murder by poisoning, for which use it has a long and continuing history in both literature and fact. Barium polysulfide is a fungicide and acaricide used in fruit and grape growing. Bismuth compounds have been used because of their astringent, antiphlogistic, bacteriostatic, and disinfecting actions. In dermatology bismuth subgallate is still used in vulnerary salves and powders as well as in antimycotics.[9] In the past, bismuth has also been used to treat syphilis and malaria. Boric acid esters derived from glycols (Biobor JF) are being used for the control of microorganisms in fuel systems containing water.
Indian tradition holds that water stored in brass pitchers prevents disease. Brass vessels release a small amount of copper ions into stored water, thus killing fecal bacterial counts as high as 1 million bacteria per milliliter. Copper sulfate mixed with lime is used as a fungicide and antihelminthic.[13] Copper sulfate is used chiefly to destroy green algae (algicide) that grow in reservoirs, stock ponds, swimming pools, and fish tanks. Copper 8-hydroxyquinoline is sometimes included in paint to prevent mildew. Gold is used in dental inlays and inhibits the growth of bacteria. Physicians prescribed various forms of lead to heal ailments ranging from constipation to infectious diseases such as the plague. Lead was also used to preserve or sweeten wine.[16] Lead arsenate is used in insecticides and herbicides.[17] Some organic lead compounds are used as industrial biocides: thiomethyl triphenyllead is used as an antifungal agent, cotton preservative, and lubricant additive;
thiopropyl triphenyllead as a rodent repellant; tributyllead acetate as a wood and cotton preservative; tributyllead imidazole as a lubricant additive and cotton preservative. Phenylmercuric borate and acetate were used for disinfecting mucous membranes at an effective concentration of 0.07% in aqueous solutions. Due to toxicological and ecotoxicological reasons phenylmercury salts are no longer applied nowadays. Nevertheless, surgeons use mercurochrome even today and despite toxicological objections.[2] Dental amalgam used in fillings inhibits bacterial reproduction. Organic mercury compounds have been used as topical disinfectants (thimerosal, nitromersol and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Mercury was used in the treatment of syphilis. Calomel was commonly used in infant teething powders in the 1930s and 1940s. Mercurials are also used agriculturally as insecticides and fungicides. The toxicity of nickel to bacteria, yeasts, and fungi differs considerably.
The metabolism of bacteria is adversely affected by silver ions at concentrations of 0.01–0.1 mg/L. Therefore, even less soluble silver compounds, such as silver chloride, also act as bactericides or germicides, but not the much less soluble silver sulfide. In the presence of atmospheric oxygen, metallic silver also has a bactericidal effect due to the formation of silver oxide, which is soluble enough to cause it. Bactericidal concentrations are produced rapidly by adding colloidal silver, which has a high surface area. Even objects with a solid silver surface (e.g., table silver, silver coins, or silver foil) have a bactericidal effect. Silver drinking vessels were carried by military commanders on expeditions for protection against disease. It was once common to place silver foil or even silver coins on wounds for the same reason. Silver sulfadiazine is used as an antiseptic ointment for extensive burns. An equilibrium dispersion of colloidal silver with dissolved silver ions can be used to purify drinking water at sea.
[2] Silver is incorporated into medical implants and devices such as catheters. Surfacine (silver iodide) is a relatively new antimicrobial for application to surfaces. Silver-impregnated wound dressings have proven especially useful against antibiotic-resistant bacteria. Silver nitrate is used as a hemostatic, antiseptic and astringent. At one time, many states required that the eyes of newborns be treated with a few drops of silver nitrate to guard against an infection of the eyes called gonorrheal neonatal ophthalmia, which the infants might have contracted as they passed through the birth canal. Silver ions are increasingly incorporated into many hard surfaces, such as plastics and steel, as a way to control microbial growth on items such as toilet seats, stethoscopes, and even refrigerator doors. Among the newer products being sold are plastic food containers infused with silver nanoparticies, which are intended to keep food fresher, and silver-infused athletic shirts and socks, which are claimed to minimize odors.
Thallium compounds such as thallium sulfate have been used for impregnating wood and leather to kill fungal spores and bacteria, and for the protection of textiles from attack by moths.[22] Thallium sulfate has been used as a depilatory and in the treatment of venereal disease, skin fungal infections, and tuberculosis. Tetrabutyltin is used as an antifouling paint for ships, for the prevention of slimes in industrial recirculating water systems, for combating freshwater snails that cause bilharzia, as a wood and textile preservative, and as a disinfectant. Tricyclohexyltin hydroxide is used as an acaricide. Triphenyltin hydroxide and triphenyltin acetate are used as fungicides. Zinc oxide is used as a weak antiseptic (and sunscreen), and in paints as a white pigment and mold-growth inhibitor.[25] Zinc chloride is a common ingredient in mouthwashes and deodorants, and zinc pyrithione is an ingredient in antidandruff shampoos. Galvanized (zinc-coated) fittings on roofs impede the growth of algae.