A Discussion of Silver as an Antimicrobial Agent: Alleviating the Confusion
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Silver used as an antimicrobial agent has an impressive history. Silver (as well as copper) is used as a disinfectant in hospital and hotel water sanitization systems. It is used in the food industry in chicken farming and oyster cleaning to inhibit bacterial and fungal growth and in the space program to sterilize recycled water aboard the MIR space station and the NASA space shuttle.1 Although not employed in allopathic mainstream medicine, colloidal silver taken orally has been used as a complementary health aid, the overuse of which in some cases has lead to argyria (also referred to as “blue skin disease,” where the reduced silver is deposited in dermal cells. This explains how the term “blue blood” originated). Silver also is used as a preservative in cosmetics and toiletries and has been incorporated into plastics of various forms to protect against microbial contamination.
Silver has a long medicinal history, going as far back as ancient Greece and Rome, when silver coins dropped into water served as a disinfectant.2 As early as 1884, Crede, a German obstetrician, used a 1% silver nitrate solution to eliminate blindness in newborns caused by post-partum infection.3 In 1887, von Behring used the same compound to treat typhoid and anthrax. In 1964, Moyer4 first used silver in the burn arena; 4 years later, Fox5 brought silver sulfadiazine (SSD) to medicine. Silver-coated catheters have been used to stem biofilm formation and prevent infection.6
Over the last 3 to 5 years, an influx of “next generation” silver-based antimicrobial dressings has been introduced into the medical arena. A review of the literature, performed over the last 3 years using references going back 30+ years to the present (key words included resistance, strains, kill rate, dissociation, biofilm) along with time spent with clinicians, reveals specific areas of confusion with respect to silver as an antimicrobial agent — specifically, silver resistance, silver dissociation, silver concentration, strains of pathogens, rate of kill, and cytotoxicity of silver. These topics will be reviewed using available publications from the peer-reviewed literature, professional presentations, and independent data.
Although some authors downplay silver resistance, the majority of authors place a fair amount of emphasis on this issue.7-31 Ovington7 writes, “Although silver has been used effectively for centuries as an antimicrobial agent, we should not assume that bacterial resistance to silver will never become a problem. The genetic basis of bacterial resistance to silver has been identified in specific bacterial isolates and closely related gene sequences have been identified in other bacteria. With silver being used more extensively in both environmental and clinical applications — particularly in wound management — the threat of resistance is not unlikely and urges for prudent use of topical antimicrobial products of any type.” In another paper, Ovington32 theorizes that resistance to silver (an antiseptic) is possible, but is less common than resistance to antibacterial agents.
Based on their own and additional research,8,9,11,12,15,17,19,21,23-26,29,33 Gupta and Silver,8 in a literature review/commentary, both state that “silver resistance is important to monitor, because modern technology has developed a wide range of products that depend on silver as a key microcidal component.” According to Levy,9 “the widespread use of silver could result in more bacteria developing resistance, analogous to the emergence of antibiotic- and biocide-resistant bacteria.”
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