ASTM E2180-18. Standard Test Method for Determining the Activity of Incorporated Antimicrobial Agent(s) In Polymeric or Hydrophobic Materials.
Test accredited by ENAC (Spanish National Accreditation Entity).
Polymeric materials such as vinyl fabrics, shower curtains and various medical devices are usually treated with antimicrobial agents. These antimicrobial agents require contact with the microbial cell to exert its maximum activity. When bacterial inoculum is applied on the surface of plastics or other hydrophobic materials with incorporated preservatives, the surface tension of the polymer generally causes the microbial suspension of inoculum to separate from its surface, so that the microorganisms in the suspension may not contact the treated surface. To get the suspension of bacteria, or other microorganisms, to contact uniformly with the surface treated with antimicrobials, in this test the inoculum is placed in a mixture with agar, in order to decrease the surface tension forming a pseudomembrane that provides a more intimate contact with the evaluated surface. This method also makes it possible to evaluate the useful life or the duration of the activity of the incorporated antimicrobial agent by testing washed or unwashed samples over a period of time.
To evaluate the antibacterial activity, the solution of molten agar is inoculated with a standardized culture of Staphylococcus aureus, Pseudomonas aeruginosa or Klebsiella pneumoniae. In addition, yeasts or fungal conidia can be used if the levuricidal or antifungal activity is to be evaluated. The usual contact time is 24 hours, but can be modified according to the manufacturer's requirements up to 96 hours to deal with more resistant microorganisms. After the chosen contact time has elapsed, the microorganisms are eluted in a neutralizing solution and the percentage of recovery compared with the respective controls is calculated.