Study Evaluates Antimicrobial Power of Silver-Ions Under Various Conditions

August 26, 2009


Results indicate that compounds are less effective at room temperature

NEW YORK, NY-Silver and copper have been used for their antimicrobial properties for centuries. Now manufacturers are incorporating these metals into consumer products and making antimicrobial claims. In particular, there are several companies that create silver-ion coatings that can be applied to various surfaces, from countertops to door knobs, which are then touted as antimicrobial; some products claim to be effective against MRSA, a frequent cause of deadly hospital-acquired infections. A study published in the most recent issue of Letters in Applied Microbiology answers the question of whether these applications work under real-life conditions.

Materials containing silver-ions have been shown to be effective under conditions of high temperature (35 degrees C, 95 degrees F) and high humidity (90 percent or higher relative humidity), but until this study they had not been tested at lower temperature and humidity levels typical of indoor environments, such as those found in hospitals. The researchers used copper alloys as a point of comparison because laboratory testing has shown that they are effective in reducing over 99.9 percent of bacteria* within two hoursat room temperature (22 degrees C, 71.6 degrees F) and normal humidity. (* Testing demonstrates efficacy against Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), E. coli O157:H7, Enterobacter aerogenes and Pseudomonas aeruginosa.)

The study tested survival rates of MRSA on two types of silver-ion coated surfaces, five copper alloy surfaces and a stainless steel surface. The silver ion materials showed only minimal bacterial reduction at 20 degrees C, 68 degrees F and 22 percent humidity. The stainless steel, which served as the experimental control, showed no measurable antimicrobial efficacy at any temperature or humidity level, as was expected.

This lack of antimicrobial activity may explain why silver-ion-based surface coating products have not been registered with the U.S. Environmental Protection Agency as an antimicrobial product for which public health claims may be made. This stands in marked contrast to the fact that copper, brass and bronze alloys were registered to make certain public health claims after EPA review of detailed data regarding the antimicrobial efficacy of the copper alloys against Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), E. coli O157:H7, Enterobacter aerogenes and Pseudomonas aeruginosa.

Copper's antimicrobial performance in laboratory settings, has made it the focus of clinical trials now underway at three U.S. hospitals. The participants, Memorial Sloan-Kettering Cancer Center in New York, the Medical University of South Carolina and the Ralph H. Johnson VA Medical Center, both in Charleston SC, have replaced plastic, aluminum and stainless steel surfaces in certain intensive care units with antimicrobial copper. The surfaces replaced are those that testing has shown to be most heavily contaminated and which also happen to be in closest proximity to the patient: IV poles, bed rails, call buttons, tray tables and armchairs.

The trials are funded by the U.S. Department of Defense under the aegis of the Telemedicine and Advanced Technologies Research Center (TATRC), a section of the Army Medical Research and Materiel Command (USAMRMC).