Antimicrobial Activity Testing Methods for Hydrophobic Patterned Surfaces

Background: One strategy to decrease the incidence of hospital-acquired infections is to avoid the survival of pathogens in the environment by the development of surfaces with antimicrobial activity. To study the antimicrobial behaviour of active surfaces, different approaches have been developed of which ISO 22916 is the standard. Aim: To assess the performance of different testing methodologies to analyse the antimicrobial activity of hydrophobic surface patterned plastics as part of a Horizon 2020 European research project (FLEXPOL: Antimicrobial FLEXible POLymers for its use in hospital environments No. 721062).Methods: Four different testing methods were used to study the antimicrobial activity of a patterned film, including the ISO 22916 standard, the immersion method, the touch-transfer inoculation method, and the swab inoculation method, this latter developed specifically for this project.Findings: The non-realistic test conditions of the ISO 22916 standard showed this method to be non-appropriate in the study of hydrophobic antimicrobial patterned surfaces. The immersion method also showed no differences between patterned films and smooth controls due to the lack of attachment of testing bacteria on both surfaces. The antimicrobial activity of films could be demonstrated by the touch-transfer and the swab inoculation methods that more precisely mimicked the way of high-touch surfaces contamination. Conclusion: The touch-transfer and the swab inoculation methods proved to be the best methodologies to test the antimicrobial activity of patterned hydrophobic surfaces. In our opinion, a new ISO standard should be developed on the basis of these tests to study the antimicrobial behaviour of patterned surfaces.