Copper coatings retain antibacterial effect in public spaces

Copper coatings retained their antibacterial effectiveness more consistently than other tested surfaces in public settings, according to a doctoral thesis defended at the University of Tartu, ERR reported.

Harleen Kaur, who defended her thesis at the university’s Institute of Molecular and Cell Biology, compared copper, silver and quaternary ammonium compound-based surfaces on door handles, shopping basket handles and café tables.

Many materials that performed well in laboratory tests were less effective in everyday conditions. Their performance was reduced by repeated cleaning, changes in humidity, wear and invisible dirt accumulating on surfaces.

In standard laboratory tests, researchers usually apply a bacterial solution to a surface and cover it with a film, keeping the sample moist and in contact with the material for up to 24 hours. Kaur said in her thesis that such wet tests can significantly overestimate the activity of surfaces intended for use in dry indoor environments.

In humid conditions, several coatings were highly effective, but most quickly lost their antibacterial activity in dry air or on dirty surfaces. Copper was the exception, maintaining its effect regardless of environmental conditions. Its impact was most evident against bacteria associated with people.

Antimicrobial materials must demonstrate that they can reduce the number of microbes by at least 99.9 percent before wider use. Ordinary cleaning and disinfecting products can keep surfaces clean for some time, but microbes may recolonise them within a few hours and spread through further contact.