Compounds extracted from larch, birch bark, Douglas fir, and alder woods with four different solvents: Effects on five skin-related microbes

Wood is an important natural resource, and the extracts of specific wood species might have growth-inhibiting effects on certain microbes. This property can be used in the pharmaceutical industry to develop phytochemical-based medicine to treat skin infections. Thus far, methanol, intrinsically toxic, has been the main solvent used for extraction of soluble wood compounds. In this study, the focus was placed on biocompatible solvents, including dimethyl sulfoxide, distilled water, and glycerin, in addition to methanol used to extract compounds from larch, birch bark, Douglas fir, and alder wood sawdust. Microbial growth was tested on four different bacterial strains and one type of fungi representing species that can affect the skin. The results revealed intrinsic toxicity of biocompatible solvents at low concentrations as well as an additive or synergistic effect of wood extracts. In particular, larch and birch extracts strongly decreased microbial growth. In addition, interference of the extract color on the measurements was observed, which must be taken into account to ensure correct analysis of the data. In conclusion, biocompatible solvents in conjunction with larch and birch extracts exhibited antimicrobial effects. The importance of solvent toxicity and background staining were highlighted to determine potential antimicrobial effects.