The use of copper and silver in carbon point-of-use filters for the suppression of Legionella throughput in domestic water systems

Abstract

Aims: To evaluate throughput of seeded Legionella pneumophila bacteria in domestic point‐of‐use filters. Methods and Results: The filters were challenged with tap water seeded with Leg. pneumophila. After multiple challenge events (4·25 × 1011 CFU per filter), the levels of Legionella were lower in the effluent from the filter containing both copper and silver (mean 4·48 × 103 CFU ml−1) than in the effluent from the filter containing copper only (1·26 × 104 CFU ml−1; P < 0·001). After a single challenge event of approx. 5 × 109 CFU L. pneumophila per filter, there was no significant difference between the levels of Legionella in the effluents from a carbon filter containing copper and a carbon filter with no metals (mean 6·87 × 102 and 6·89 × 102 CFU ml−1, respectively; P = 0·985). Conclusions: Legionella was detected in filter effluent up to 6 weeks after being challenged, indicating that while filters may reduce the levels during an initial contamination event, the exposure is extended as the accumulated bacteria slough off over time. Significance and Impact of the Study: This study has provided an understanding of the response of Legionella to the use of silver and copper in domestic point‐of‐use carbon filters.

A Concept in Bactericidal Materials: The Entrapment of Chlorhexidine within Silver

“…[5] Nowadays silver and its compounds are commonly used in many domains: In the clinical area, silver impregnated dressings are used in wound management, particularly in burns and in chronic and diabetic ulcers, [6] and in catheters and other implantable medical devices. [7] Non-clinical applications include its use in water purification processes (such as the Katadyn process [8] ), for impregnation of carbon filters, [9,10] in coated domestic appliances, [11,12] in swimming pool electrochemical sanitation, [13] in textiles, [14] as food preservatives, [9,15] in cosmetic preparations, [16] and as nano-silver in computer components. [12] The biocidal activity of metallic silver is associated with its potency at very low concentrations, defined by Carl Nageli as oligodynamic: [17][18][19] bulk silver releases trace amounts of silver cations from its surface, which are strongly toxic to a wide range of microorganisms including gram negative and gram positive bacteria, fungi, and even viruses.…”

Clean Water for Developing Countries

“…Metal-coated filters were found to be more efficient as compared with filters without metals. However, the bacteria was detected even after six weeks of the challenge, indicating that after the initial decrease in the number of bacteria, sloughing from the filters resulted in an increase of bacterial load (46).…”

Inexpensive mineral copper materials with antibacterial surfaces

“…Silver has been extensively investigated for commercial applications because it can be effective at a lower concentration. 11,27 However, silver is much more expensive, and its biological activity drops to a negligible value at temperature above 75°C, unlike copper. 28,29 In addition, although both copper and silver are effective antimicrobial materials against MRSA at room temperature and elevated relative humidity, silver loses its efficacy at low humidity.…”

“…7 Copper has been proven to be biostatic and effectively inhibits the growth of harmful bacteria without any additional treatment. [8][9][10] Copper inactivates harmful microbes including L. pneumophila, methicillin-resistant Staphyloccous aureus ("staph"), Escherichia coli, Listeria monocytogenes 5,[11][12][13][14] and many other microbes as recently reviewed by Borkow. 15 For this reason, the number of copper-bearing products -medical tools and hygienic devices, oral hygiene products, antiseptics, paints and others -has exploded in recent years.…”