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

Abstract

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.

Copper as an antimicrobial agent: recent advances

“…36,78,92 Other experimental conditions which vary between studies and are known to affect microbial susceptibility to copper include factors that affect inoculum-drying time, like temperature, airow and humidity. 21,88,[93][94][95] Issues with the lack of 'real world' conditions in the industrial standard tests (e.g., ISO 22196, ISO 21702, ISO 846) and the vast collection of modied protocols that now exist as a result have been previously acknowledged and adequately discussed. 21,93,96,97 In addition, the need to take into account the effect of cleaning protocols, surface soiling and wear on material efficacy has been documented.…”

“…21,88,[93][94][95] Issues with the lack of 'real world' conditions in the industrial standard tests (e.g., ISO 22196, ISO 21702, ISO 846) and the vast collection of modied protocols that now exist as a result have been previously acknowledged and adequately discussed. 21,93,96,97 In addition, the need to take into account the effect of cleaning protocols, surface soiling and wear on material efficacy has been documented. 93,97 We reiterate previous recommendations calling for updated industrial standard tests which apply environmental parameters more reective of actual conditions within the healthcare setting.…”

“…21,93,96,97 In addition, the need to take into account the effect of cleaning protocols, surface soiling and wear on material efficacy has been documented. 93,97 We reiterate previous recommendations calling for updated industrial standard tests which apply environmental parameters more reective of actual conditions within the healthcare setting.…”

Antibacterial activity testing methods for hydrophobic patterned surfaces

“…It has been demonstrated that the micro-patterned surface of films reduces bacterial contamination 7 . To evaluate the antibacterial activity of patterned films different tests can be used and depending on the methodology used, the antibacterial activity results could vary 7 , 16 – 18 .…”

How Do We Determine the Efficacy of an Antibacterial Surface? A Review of Standardised Antibacterial Material Testing Methods

“…Environmental conditions such as these can alter the efficacy of an AMM, and therefore careful consideration should be given when designing or interpreting data from an antimicrobial test method. Humidity-Humidity is an important determinant for the drying time of liquid droplets [79], and therefore is most likely linked to AMM efficacy. In most cases, a reduction in the humidity of the AMM results in a lower antimicrobial efficacy because of the reduction in moisture at the surface through evaporation.…”