Survival of epidemic strains of nosocomial- and community-acquired methicillin-resistant Staphylococcus aureus on coins

Abstract

Background: The aim of this study was to examine the survival dynamics of several epidemic nosocomial and community-acquired methicillin-resistant Staphylococcus aureus (MRSA) strains on copper alloy coins.

Methods: Six different phage types of nosocomial MRSA (Irish 1, Irish 2, EMRSA 15, EMRSA 16, distinct type, and untypeable), as well as community-acquired MRSA, were examined in this study. Two isolates of each type were studied, resulting in a total of 14 organisms being examined. Cells were harvested from overnight cultures of Columbia blood agar (Oxoid) supplemented with 5% (wt/vol) defibrinated blood to make a 0.5 McFarland inoculum standard. An inoculum of each MRSA isolate in 5-microl volume was added to washed, dried, and presterilized 1-penny copper-plated steel coins, equating to log(10) 5 colony-forming units (cfu) and allowed to dry naturally at ambient temperatures in the dark.

Results: Recovery experiments were unable to isolate any of the inoculated organisms 4 hours postinoculation. To ascertain whether this was a toxic effect from the copper alloy of the coins or a physical desiccation effect, experiments were repeated on glass and plastic, and similar results were demonstrated. The effect of soil was investigated by repeating the experiment with (60)Co irradiated pus and sterile blood, and we were able to demonstrate the survival of all organisms after at least 2 weeks storage in the dark at ambient temperature, during which the quantitative counts were reduced by approximately 1-log unit and 2-log units for blood and pus, respectively.

Conclusion: This study demonstrates that all epidemic nosocomial- and community-acquired MRSA do not survive when no organic protection is offered but survive well when soil (pus and blood) is present, thus offering protection from drying. This study indicates that contaminated coins may serve as potential vehicles for MRSA.