On 19 August at 14:15 Harleen Kaur will defend her doctoral thesis “Performance of antimicrobial surfaces under application-relevant conditions” for the award of the degree of Doctor of Microbiology.
Supervisors:
Professor Angela Ivask, University of Tartu
Professor Vambola Kisand, University of Tartu
Opponent:
Tomas Kačergius, PhD, Vilnius University (Lithuania)
Summary:
Antimicrobial surfaces are increasingly used in healthcare, public, and other shared indoor environments to reduce microbial contamination on frequently touched surfaces. Their main advantage is continuous antimicrobial activity between routine cleaning events. However, standardized laboratory results do not always reflect real-life performance, where surfaces are exposed to drying, humidity changes, organic residues, repeated touching, cleaning, abrasion, and complex microbial communities. This thesis evaluated antimicrobial surfaces under application-relevant conditions, focusing on antibacterial efficacy, durability after simulated wear, and effects on microbial communities on real high-touch surfaces. The studied materials included copper- and silver-based surfaces, quaternary ammonium based (SiQAC) coatings, ZnO- and TiO₂-based photocatalytic coatings, and visible-light-activated AgSbSe₂ thin films. The results showed that antibacterial performance strongly depended on test conditions. Relative humidity, inoculum format, and organic soiling had major effects, and conventional wet-film tests may overestimate antimicrobial activity by creating favourable moist conditions. Copper showed the most consistent antibacterial effect, while silver- and SiQAC-based surfaces were more condition-dependent. ZnO based coating durability tests showed that simulated wear could either improve or reduce activity: abrasive treatment increased activity, likely by exposing active ZnO material, whereas rubbing tended to mask active sites. AgSbSe₂ thin films showed visible-light-driven antibacterial activity against E. coli, suggesting their usability in indoor lighting conditions. In real-life pilot studies, copper tape on shopping basket handles showed the clearest effect by reducing bacterial load and changing microbial community structure. TiO₂ based coatings reduced microbial load in some cases, while silver- and SiQAC-based surfaces showed limited or site-dependent effects. Overall, this thesis demonstrates that the performance of antimicrobial surfaces depends strongly on the tested conditions. Future evaluation of antimicrobial surfaces should combine realistic efficacy testing, durability assessment, and microbiome-level analysis to better understand their practical value in healthcare and public environments.
