Vaccinium myrtillus leaves and Frangula alnus bark derived extracts as potential antistaphylococcal agents

Due to constantly increasing antibiotic resistance of pathogens and participation of the biofilms they make in various types of infections, a development of alternative therapeutic strategies becomes an urgent need. Taking advantage of the biological activity of plant-derived compounds can solve this problem. In this study antimicrobial, including those synergistic with classic antibiotics, and cytotoxic properties of newly-obtained extracts from Vaccinium myrtillus leaves (VLE) and Frangula alnus bark (FBE) were evaluated. Both tested extracts exhibited relevant antistaphylococcal activity (MIC range 0.75-1.5 mg/mL) accompanied by a relativly low cytotoxic effect on mammalian cells (BI > 1). Phytochemical analysis of the extracts tested showed a high total content of phenolic compounds with the predominance of hydroxycinnamic acids in VLE and hydroxybenzoic acids and flavanols in FBE. Widely described in the literature antimicrobial properties of phenolics were probably connected with the biological activity of the extracts tested. We also report that the presence of VLE or FBE at sub-MIC concentrations enhances biocidal potential of vancomycin and linezolid. Therefore, we are considering a possibility of an alternative therapy for local infections caused by S. aureus by combining classic antibiotics with plant-derived extracts.