Environmental Advances (Oct 2023)
Touch the wood: Antimicrobial properties of wooden and other solid material surfaces differ between dry and moist contamination in public and laboratory exposure
Abstract
Several bacteria causing infections can remain infectious on surfaces from hours to several days and weeks. Antibacterial properties of wood are poorly understood in terms of dry contamination via hands, as large majority of previous research has been carried out by using liquid inoculation methods. The effects of wood surface treatments on antimicrobial activity require more investigation. Here, antimicrobial properties of surfaces of 18 different every-day indoor materials, i.e., non-treated wooden surfaces, wood with surface and other treatments, and other solid indoor materials were examined. This study is unique, as the materials that were exposed to human contact in public space were also investigated in controlled conditions for their antibacterial properties. First, bacterial loads of different material surfaces were quantified in a real-life public setting by contact plate method. Secondly, in a controlled exposure chamber trial, bacterial viability of Staphylococcus epidermidis and Bacillus aerius/licheniformis was followed as a function of time after spreading bacterial aerosols on samples. In the public exposure, non-wood coatings/materials (tile, laminate, vinyl cork, lacquer coated wood) with non-porous surfaces had the lowest number of bacterial colonies forming units (cfu). Differences in cfu were also observed between the wood species: the lowest accounts were recorded from white oak, and black walnut. In the exposure chamber trial, the viability of S. epidermidis decreased on almost all study materials, with the lowest viability detected from non-treated white oak. Instead, B. aerius/licheniformis remained stable on most material surfaces. The differences in results in wood antibacterial properties between the dry and moist contamination may be explained by the fact that moist aerosol inoculum faces both passive and active antimicrobial mechanisms of non-treated wood; porous wood structure dries bacteria, and wood chemical constituents possess bacteriostatic efficacies. In dry conditions via hand contamination, instead, microbes may adhere more on porous surfaces than on non-porous ones.
