Metallic Copper as an Antimicrobial Surface

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Gregor Grass, Christopher Rensing, and Marc Solioz

Conclusions

The antimicrobial properties of copper surfaces have now been firmly established. Hospital trials have shown a reduction in bacterial counts, indicating that copper surfaces are a promising additional tool alongside other hygienic measures to curb the number and severity of hospital-acquired infections. At this point, additional studies would be helpful in determining the most cost-effective way to give maximal protection in hospitals. For example, should only highly frequented sites be made of copper, e.g., doorknobs, faucets, and bed rails, or should the majority of accessible surfaces be made of copper? In addition, different copper alloys should be tested not only for their effectiveness but also for their esthetic appeal. Finally, the antimicrobial properties of copper surfaces must be integrated with other methods of disinfection and the overall hygiene concept of a health care facility. Additional measures, such as the addition of spore germinants to cleaning solutions to improve killing of spores, also deserve further investigation.

Bacterial resistance is a major concern in infection control. Are there bacteria which are naturally refractory to contact killing by copper? It is known that live bacteria can be isolated from copper-containing surfaces, and in a recent study, 294 isolates from European 50-cent coins were investigated in regard to copper resistance. Some of the isolates indeed exhibited prolonged (1 to 3 days) survival on dry but not on moist copper surfaces, but none of the strains was exceptionally copper resistant in culture (12). Survival on copper-containing coins appeared to be the consequence of either endospore formation, survival on patches of dirt, or a special ability to endure a dry metallic copper surface. While the latter, rare property is not yet understood, widespread appearance of bacterial resistant to contact killing appears unlikely for the following reasons:

(i) plasmid DNA is completely degraded after cell death by contact killing, preventing the transfer of resistance determinants between organisms (39),

(ii) contact killing is very rapid, and cells are not dividing on copper surfaces, precluding the acquisition of resistance, and

(iii) copper and copper alloys have been used by humans for thousands of years, yet no bacteria fully resistant to contact killing have been discovered.

Sources

12. Espirito Santo, C., P. V. Morais, and G. Grass, 2010. Isolation and characterization of bacteria resistant to metallic copper surfaces. Appl. Environ. Microbiol. 76:1341-1348.

39. Warnes, S. L., S. M. Green, H. T. Michels, and C. W. Keevil, 2010. Biocidal efficacy of copper alloys against pathogenic enterococci involves degradation of genomic and plasmid DNA. Appl. Environ. Microbiol. 76:5390-5401.