Context-dependent effects of antimicrobial coatings on microbial load and bacterial community composition on public high-touch surfaces

BackgroundAntimicrobial surfaces incorporated into high-touch public areas are used as a passive intervention to reduce surface microbial load and reduce the spread of infections. However, usually such surfaces lack proof of their antimicrobial activity in real use conditions and against a wider variety of microbes. This study evaluated the real-world performance of copper, TiO2-, silver- and quaternary ammonium compound (SiQAC)-based surfaces, which are commercially available and have proven antibacterial activity in lab tests. The surfaces were introduced to five study sites in diverse environments to collect data on bacterial load, community structure and taxonomic profile over several months. ResultsCopper surfaces introduced to shopping basket handles consistently exhibited the strongest antimicrobial performance, with significant reductions in aerobic bacterial counts and bacterial DNA, accompanied by clear shifts in microbial community composition. These shifts included reduction of several human-associated and opportunistic taxa and relative enrichment of environmentally resilient, stress-tolerant genera. TiO2-based photocatalytic coating reduced bacterial load in kindergarten tables under field conditions but did not significantly alter overall community structure. Silver-based surfaces on university campus tables showed minimal effects on microbial load and composition despite confirmed antibacterial activity in laboratory testing. Analogously to silver, SiQAC-based coating despite being active in lab conditions showed no decrease in bacterial load in real use conditions. When applied onto cafeteria and animal clinic tables SiQAC coating displayed context-dependent effects, with modest, genus-specific changes and increased richness in a high-contact cafeteria environment, but no significant impact in a low-biomass animal clinic setting. Viability based analysis revealed that on most of the surfaces a notable fraction of detected microbial DNA originated from non-viable cells. ConclusionsThis multisite field study demonstrates that the real-world performance of antimicrobially coated surfaces is strongly context dependent and cannot be reliably predicted from laboratory testing alone. Moreover, to understand the effect of antimicrobial coatings on surface microbial communities, real-use monitoring is needed.