Biocidal Efficacy of Copper Alloys against Pathogenic Enterococci Involves Degradation of Genomic and Plasmid DNAs



Appl Environ Microbiol, August 2010; 76(16): Page 5390–5401

American Society for Microbiology


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US Government National Center for Biotechnology Information

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S. L. Warnes, S. M. Green, H. T. Michels, and C. W. Keevil


"Although all of the alloys are very effective at killing control and clinical strains of E. faecium, compared to stainless steel, survival appears to be related to the percentage of copper in the alloys (Fig. ​(Fig.1).1). The most rapid killing occurs on pure copper and alloys containing >90% copper (C51000 and C70600), with increased survival times on the remaining alloys containing 60 to 70% copper (C28000, C75200, and C26000) (Fig. ​(Fig.1).1). Alloys containing >95% copper (C51000, C70600) were as effective as pure copper for isolates 2 and 3, resulting in cell death at 1 h, but small numbers of cells of isolates 1and 4 remained viable (86% similarity) at up to 2 h after contact. Viable cells of all of the isolates were detected following 2 h of contact with alloy C28000, which has the lowest copper content tested here (60%). There are, however, exceptions: viable cells of clinical isolate 3 were detected following 2 h of contact on alloy C26000 (cartridge brass, 70% copper), but C75200 (nickel silver), which contains 5% less copper, was a more effective bactericidal surface."


"There has been much concern recently that the frequency of antimicrobial resistance in bacteria has increased in concert with increasing usage of antimicrobial compounds. A recent European Commission report (16) has summarized the scientific evidence from bacteriological, biochemical, and genetic data indicating that the use of active molecules in biocidal products may contribute to the increased occurrence of antibiotic-resistant bacteria. The selective stress exerted by biocides may favor bacteria expressing resistance mechanisms and their dissemination. Some biocides have the capacity to maintain the presence of mobile genetic elements that carry genes involved in cross-resistance between biocides and antibiotics. In enterococci, up to 25% of the genome has been found to contain mobile elements (41). The dissemination of these mobile elements, their genetic organization, and the formation of biofilms provide conditions that could create a potential risk of development of cross-resistance between antibiotics and biocides. The case for the use of copper in antimicrobial products was considered, but there was no evidence that this might lead to antibiotic resistance in the way that the widespread use of Triclosan has been associated with the emergence of triclosan and mupirocin resistance in MRSA, although evidence for this is limited (15, 16, 44). The plasmid-localized copper resistance tcrB gene has been identified in E. faecium and E. faecalis thought to originate from pigs fed with copper sulfate-supplemented food (19). The Tn1546 element and erm genes conferring glycopeptide and macrolide resistance are located on the same plasmid, but there is no significant evidence that use of copper in animal feeds coselected for antibiotic resistance (20) except under experimental conditions in piglets fed a high concentration of copper sulfate (21). However, continued use of copper sulfate was not able to maintain high levels of antimicrobial resistance (21).

The current study indicates that DNA is rapidly destroyed in enterococci exposed to copper surfaces, meaning that there is little chance of high-level copper or antibiotic resistance developing. Consequently, this disintegration of bacterial nucleic acid supports the use of copper alloys as contact surfaces in clinical environments to actively kill bacterial cells without the occurrence of DNA mutation and transfer of genetic material carrying antibiotic resistance genes."


15 European Commission. 2002. Opinion on triclosan resistance. European Commission Health & Consumer Protection Directorate-General, Brussels, Belgium.

16 European Commission. 2009. Assessment of the antibiotic resistance effects of biocides. Scientific Committee on Emerging and Newly Identified Health Risks, Brussels, Belgium.

19 Hasman, H., and F. M. Aaresstrup. 2002. tcrB, a gene conferring transferable copper resistance in Enterococcus faecium: occurrence, transferability and linkage to macrolide and glycopeptide resistance. Antimicrob. Agents Chemother. 46:1410-1416.

20 Hasman, H., and F. M. Aaresstrup. 2005. Relationship between copper, glycopeptide, and macrolide resistance among Enterococcus faecium strains isolated from pigs in Denmark between 1997 and 2003. Antimicrob. Agents Chemother. 49:454-456.

21 Hasman, H., I. Kempf, B. Chidaine, R. Cariolet, A. J. Ersboll, H. Houe, H. C. B. Hansen, and F. M. Aaresstrup. 2006. Copper resistance in Enterococcus faecium, mediated by the tcrB gene, is selected by supplementation of pig feed with copper sulfate. Appl. Environ. Microbiol. 72:5784-5789.

31 Macomber, L., C. Rensing, and J. A. Imlay. 2007. Intracellular copper does not catalyze the formation of oxidative DNA damage in Escherichia coli. J. Bacteriol. 189:1616-1626.

41 Paulsen, I. T., L. Banerjei, G. S. A. Myers, K. E. Nelson, R. Seshadri, T. D. Read, D. E. Fouts, J. A. Eisen, S. R. Gill, J. F. Heidelberg, H. Tettelin, R. J. Dodson, L. Umayam, L. Brinkac, M. Beanan, S. Daugherty, R. T. DeBoy, S. Durkin, J. Kolonay, R. Madupu, W. Nelson, J. Varmathevan, B. Tran, J. Upton, T. Hansen, J. Shetty, H. Khouri, T. Utterback, D. Radune, K. A. Ketchum, B. A. Dougherty, and C. M. Fraser. 2003. Role of mobile DNA in the evolution of vancomycin-resistant Enterococcus faecalis. Science 299:2071-2074.

44 Suller, M. T., and A. D. Russell. 2000. Triclosan and antibiotic resistance in Staphylococcus aureus. J. Antimicrob. Chemother. 46:11-18.