Antimicrobial Activity of Phenolic Compounds Extracted from <em>Platanus hybrida</em>: Exploring Alternative Therapies for a Post-Antibiotic Era

Abstract

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 plantderived 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 antimicrobial activity against antibiotic resistant bacterial strains. The polyphenolic compounds 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 mg/mL. Antimicrobial susceptibility assay was performed using Kirby-Bauer disc diffusion method and was tested against ten different bacteria: Listeria monocytes, Bacillus cereus, Enterococcus faecium, Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis, Salmonella enteritidis, Pseudomonas aeruginosa, Klebsiella pneumoniae and 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 S. enteritidis, E. faecium and E. faecalis. These results show that, P. hybrida's phenolic compounds act as antibacterial agents which may become useful therapeutic tools and 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.