In vitro antimicrobial activity of different Verbascum niveum extracts
Abstract
Medicinal plants are the main ingredient of numerous medicines and pharmaceutical products, and antimicrobial activity has been demonstrated in a large number of medicinal plant extracts and essential oils. Considering that Verbascum species officially approved by the European Medicines Agency show antimicrobial properties, but also that there are other species of this genus that have not been sufficiently studied, we aimed to evaluate the antimicrobial activity of six different extracts of V. niveum. Antimicrobial bioassays were performed with one fungus (Candida albicans) and four bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis) by broth microdilution method according to the recommendations of the European Committee on Antimicrobial Susceptibility Testing. The results were expressed as minimal inhibitory concentration (MIC) - the lowest concentration of a sample, usually of a drug (in our case, an extract - mg/ml), that prevents the visible growth of bacteria. Only MIC values lower than those for the solvents are considered positive results. The MIC values of all extracts against all tested bacterial strains were lower than the MIC values of the solvents, but in the case of fungi, the results were mostly similar. Thus, the extracts are effective against bacteria, but their efficacy is low against the fungal strains tested. The MIC values ranged from 0.39 to 1.25 mg/ml. The strongest effect was obtained with the ethanolic extract of leaves against Staphylococcus aureus (0.39 mg/ml). According to our result, the tested extracts have modest antimicrobial activity, although mullein is considered an excellent antimicrobial agent.
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