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Environmental and Experimental Factors Affecting Efficacy Testing of Nonporous Plastic Antimicrobial Surfaces

non porus hard surfaces

Test methods for efficacy assessment of antimicrobial coatings are not modelled on a hospital environment, and instead use high humidity (>90%) high temperature (37 °C), and no airflow. Therefore, an inoculum will not dry, resulting in an antimicrobial surface exhibiting prolonged antimicrobial activity, as moisture is critical to activity. Liquids will dry quicker in a hospital ward, resulting in a reduced antimicrobial efficacy compared to the existing test, rendering the test results artificially favourable to the antimicrobial claim of the product. This study aimed to assess how hospital room environmental conditions can affect the drying time of an inoculum, and to use this data to inform test parameters for antimicrobial efficacy testing based on the hospital ward.

The drying time of different droplet sizes, in a range of environmental conditions likely found in a hospital ward, were recorded (n = 630), and used to create a model to inform users of the experimental conditions required to provide a drying time similar to what can be expected in the hospital ward. Drying time data demonstrated significant (p < 0.05) variance when humidity, temperature, and airflow were assessed. A mathematical model was created to select environmental conditions for in vitro antimicrobial efficacy testing. Drying time in different environmental conditions demonstrates that experimental set-ups affect the amount of time an inoculum stays wet, which in turn may affect the efficacy of an antimicrobial surface.

This should be an important consideration for hospitals and other potential users, whilst future tests predict efficacy in the intended end-use environment.


Authors: James Redfern 1,,Jake Tucker 2 ,Lisa M. Simmons 2 ,Peter Askew 3 ,Ina Stephan 4 and Joanna Verran 1

School of Healthcare Science, Manchester Metropolitan University, Chester Street, Manchester M1 5GD, UK
School of Engineering, Manchester Metropolitan University, Chester Street, Manchester M1 5GD, UK
IMSL, Pale Lane, Hartley Whitney, Hants RG27 8DH, UK, (AMiCI Project)
BAM, Unter den Eichen 87, 12205 Berlin, Germany

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