Effect of Copper Surfaces

Copper and copper alloys have been studied in experiments simulating a clinical setting by using moist and dry inoculation techniques.

Many in vitro studies have demonstrated the antimicrobial effect of copper on a wide spectrum of Gram-positive bacteria (i.e., Enterococcus spp. and Staphylococcus spp.), Gram-negative bacteria (i.e., Acinetobacter spp., Campylobacter jejuni, E. coli, and Pseudomonas spp.), viruses (i.e., influenza A virus, herpes simplex virus, and human immunodeficiency virus [HIV]), and fungi and yeasts (i.e., Candida spp.).

The biocidal efficacy is dependent on the copper concentration, length of exposure, humidity, and temperature. Various studies have experimented with the copper concentration and different lengths of exposure to achieve the most efficient biocidal effect, with the majority of the research having been conducted by the research team of Keevil in Southampton, United Kingdom. They placed a higher concentration of bacteria onto coupons with different concentrations of copper ranging between 0% (100% stainless steel or 100% metallic zinc) and 100% but varying the time of surface exposure of the microbes to the metal from several minutes to up to 24 h. Viable microbes were counted after staining for visualization by epifluorescence microscopy. They demonstrated that the biocidal efficacy increases with higher copper concentrations. A significant biocidal effect was reached using metals with a copper concentration of between 55% and 100%; there was a complete eradication of microbes within 90 min on pure copper and 120 min on copper nickel with a 75% copper concentration. Copper continuously reduced microbial contamination, with a 99.9% reduction within 2 h of exposure.

Initial studies were done using a wet inoculum at high relative humidity (>90%) and incubated at high temperatures (35°C). However, as this would not reflect a clinical setting, different laboratory techniques have been used. One difference is the use of either a dry inoculum (reflecting touch contamination) or a wet inoculum (reflecting wet contamination such as a sneeze).

It was found that bacterial killing occurred more rapidly under dry conditions than under moist ones. Using a wet inoculum, bacteria such as Enterococcus faecalis or Enterococcus faecium were killed in 1 h, compared to 10 min when presenting the inocula to the metal coupons in lower volumes (20 μl). Also, the effects of temperature and relative humidity were explored.

（To be continued）

Copy from cmr.asm.org

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