Biocide impregnated surface materials for use in clinical areas – under what conditions do they work?

The survival of microorganisms on surfaces is well documented, potentially acting as a reservoir for the dissemination of healthcare-associated infections (HCAIs). Antimicrobial surfaces aim to control surface bioburden and lower HCAI rates. The existing antimicrobial surface efficacy test (JIS Z 2801) is an initial screening test; however, its set up (35°C, >90% relative humidity (RH)) bears little relationship to conditions in practice. This study aimed to develop new surface efficacy tests using wet and dried microbial inocula, reflecting conditions within a healthcare setting. Changes in surface RH, temperature and bioburden were measured over one year at a hospital, allowing realistic parameters to be set for the new tests. Wet and dry inocula tests were developed and validated to mimic aerosol deposition and dry-touch contamination on surfaces, respectively. Aerosols of S. aureus, A. baumannii and B. subtilis spores and dry inocula of S. aureus and A. baumannii were tested against copper alloys and control stainless steel surfaces. Surviving bacteria were enumerated after varying contact times, and under in-use and JIS Z 2801 test conditions. FACS experiments were conducted to understand the mechanism of action of copper against dried microbial inocula. Wet inoculum testing showed copper alloys presented significantly reduced activity against S. aureus aerosols at in-use conditions (>4 log10 after 60 min) compared to JIS Z 2801 test conditions (>4 log10 after 30 min). A >4 log10 reduction in A. baumannii was observed within 30 min but copper alloys were not sporicidal at in-use conditions. Dry inoculum testing showed a