Abstract
Tree barks are mainly considered as wood wastes from forestry activities, but represent valuable resources as they may contain antimicrobial compounds. Here, we aimed to evaluate the possible antimicrobial activities of bark extracts and to characterize the chemical composition of the most active extract. Ten methanol bark extracts were tested in vitro against 17 bacterial strains and 5 yeast strains, through minimum inhibitory concentration (MIC) and minimum bactericidal (or fungicidal) concentration (MBC/MFC) assays. The extract from Prunus avium (E2-4) displayed the largest bactericidal activity against Gram-positive bacteria, with a lethal effect on 6 out of 8 strains. Antibiofilm assays of E2-4 were performed by crystal violet staining and enumeration of adhered bacteria. Assays demonstrated a biofilm inhibitory effect of E2-4 against Staphylococcus aureus CIP 53.154 at concentrations equal to or higher than 250 µg/mL. Chemical profiling of E2-4 by 13C nuclear magnetic resonance (NMR) revealed the presence of dihydrowogonin as a major constituent of the extract. E2-4 was fractionated by centrifugal partition chromatography and the three fractions containing dihydrowogonin were tested for their antibacterial and antibiofilm activities, revealing similar activities to those of E2-4. Dihydrowogonin was positively assessed as an interesting antimicrobial compound, which could be valued from wastes of Prunus avium barks.
Highlights
The ongoing emergence of resistant bacterial strains has led to the reduced effectiveness of even newly developed antibiotics, making patients much more difficult to treat [1,2,3,4,5].As the number of multidrug-resistant bacteria continues to increase, the number of new antimicrobial molecules continues to dramatically decrease
The antibiotics used as controls confirmed that all the Gram-negative bacteria were resistant to vancomycin and that all the yeasts were sensitive to amphotericin B
Ten methanol bark extracts obtained from common temperate tree species were simultaneously evaluated for their antimicrobial activities against a panel of 22 microorganisms
Summary
As the number of multidrug-resistant bacteria continues to increase, the number of new antimicrobial molecules continues to dramatically decrease. A strategy to find solutions against antibiotic resistance relies on the investigation of natural resources from which highly active compounds may be extracted [6]. The antimicrobial compounds isolated from terrestrial or marine extracts have the ability to inhibit bacterial growth through different mechanisms, as compared to conventional antibiotics from microorganisms, and can be of significant clinical value for the treatment of human infectious diseases [7,8]
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