Effects of Temperature and Humidity on the Efficacy of Methicillin-resistant Staphylococcus aureus Challenged Antimicrobial Materials Containing Silver and Copper

Michels HT, Noyce JO, Keevil CW. Lett Appl Microbiol. 2009 Aug;49(2):191-195.

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Aims: To compare silver and copper, metals with known antimicrobial properties, by evaluating the effects of temperature and humidity on efficacy by challenging with methicillin resistant Staphylococcus aureus (MRSA).

Methods and Results: Using standard methodology described in a globally used Japanese Industrial Standard, JIS Z 2801, a silver ion-containing material exhibited >5 log reduction in MRSA viability after 24 h at >90% relative humidity (RH) at 20ºC and 35ºC but only a <0·3 log at ~22% RH and 20ºC and no reduction at ~22% RH and 35ºC. Copper alloys demonstrated >5 log reductions under all test conditions.

Conclusions: While the high humidity (>90% RH) and high temperature (35ºC) utilized in JIS Z 2801 produce measurable efficacy in a silver ion-containing material, it showed no significant response at lower temperature and humidity levels typical of indoor environments.

Significance and Impact of the Study: The high efficacy levels displayed by the copper alloys, at temperature and humidity levels typical of indoor environments, compared to the low efficacy of the silver ion-containing material under the same conditions, favours the use of copper alloys as antimicrobial materials in indoor environments such as hospitals.