In vitro comparison of methods for sampling copper-based antimicrobial surfaces

Area of Science:

• Microbiology
• Materials Science
• Infection Control

Background:

• Self-sanitizing surfaces, particularly copper (Cu), are vital for reducing pathogen transmission on high-touch surfaces.
• Accurate enumeration of bacteria is crucial for validating the antimicrobial efficacy of these surfaces.
• Existing literature lacks comprehensive studies on reliable bacterial enumeration methods for copper surfaces.

Purpose of the Study:

• To investigate the impact of bacterial collection methods on the perceived antimicrobial efficacy of copper surfaces.
• To determine if direct plating on copper influences bacterial viability and subsequent counts.
• To identify reliable methods for assessing the true antimicrobial properties of copper.

Main Methods:

• Comparison of bacterial counts obtained from direct plating of samples onto Petrifilm.
• Evaluation of bacterial counts using indirect sample collection methods from copper surfaces.
• Analysis of potential revival of stressed or dying bacteria due to direct contact with copper.

Main Results:

• Direct application of Petrifilm onto copper surfaces led to an overestimation of bacterial counts.
• This overestimation is attributed to the revival of stressed and dying bacteria on the copper surface.
• Indirect collection methods did not exhibit this revival phenomenon, yielding more accurate counts.

Conclusions:

• The method of bacterial collection significantly impacts the assessment of copper's antimicrobial efficacy.
• Direct plating on copper surfaces can lead to artifactually high bacterial counts, masking true efficacy.
• Indirect sampling methods are recommended for accurate time-kill kinetics and long-term efficacy studies of copper surfaces.