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Antimicrobial Activity of Phenolic Compounds Extracted from Platanus hybrida: Exploring Alternative Therapies for a Post-Antibiotic Era
* 1 , 1, 2, 3, 4 , 5 , 6 , 2, 3, 4 , 1, 2, 3, 4
1  Microbiology and Antibiotic Resistance Team (MicroART), Department of Veterinary Sciences, University of Trás-os-Montes and Alto Douro (UTAD), Vila Real, Portugal.
2  Department of Genetics and Biotechnology, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal.
3  Functional Genomics and Proteomics Unit, University of Trás-os-Montes and Alto Douro (UTAD), Vila Real, Portugal.
4  Associated Laboratory for Green Chemistry (LAQV-REQUIMTE), University NOVA of Lisbon, Caparica, Portugal.
5  Centre for the Research and Technology of Agro-Environmental and Biological Sciences (CITAB), University of Trás-os-Montes and Alto Douro (UTAD), Vila Real, Portugal.
6  Department of Agronomy, School of Agrarian and Veterinary Sciences, University of Trás‐os‐Montes e Alto Douro (UTAD), Vila Real, Portugal.


Multidrug-resistant bacteria are a significant threat to public health and new classes of antibiotics and approaches to treatment are needed. Several studies showed that natural plant-derived compounds could be a promising mean to fight microbial resistance but only a few were conducted with antibiotic resistant bacteria. Therefore, the aim of this study was to extract phenolic compounds from the leaves, fruits and tree trunk of Platanus hybrida and evaluate their antibacterial activity against antibiotic resistant bacterial strains.

The polyphenolic constituents were extracted using a water/ethanol (20:80) mixture. Two grams of powder of each sample was extracted with 100 mL of solvent by stirring for 2h. The extracts were redissolved in dimethyl sulfoxide (DMSO) to a final concentration of 100 μg/mL. Antimicrobial susceptibility assay was performed using Kirby-Bauer disc diffusion method and was tested against ten different bacteria: Listeria, Pseudomonas aeruginosa, Enterecoccus faecium, Klebsiella pneumoniae, Staphylococcus aureus, Salmonella enteriditis, Enterococcus faecalis, Bacillus cereus, Staphylococcus epidermidis e Escherichia coli.

The fruits had the highest antibacterial activity showing a minimum inhibitory concentration (MIC) of 10mg/mL, contrary to the tree trunk that showed the lowest antibacterial activity. None of the extracts showed antimicrobial properties against E. faecium, S. enteriditis and E. faecalis.

These results show that, Platanus hybrida’s phenolic compounds act as antibacterial agents which may become useful therapeutic tools and may represent a source for the development of novel antimicrobials. However, they were not effective against all bacteria which shows that polyphenols, alone, might not substitute antibiotics.

Keywords: polyphenols; plant-derived compounds; antimicrobial resistance; bacterial resistance; public health.