Antimicrobial Activity of Polyphenolic Compounds

Introduction. The emergence of new strains of microorganisms with multidrug resistance (MDR) is one of the most pressing problems of modern medicine. Currently, to combat MDR, active attempts are being made to obtain new biologically active substances of natural (microbial, plant, animal) origin. Earlier, 32 individual compounds were isolated by the authors from the aerial part of Iris laclea Pall., Rubus chameamorus L. leaves, Empetrum nigrum L. shoots, Ononis arvensis L. aerial part and Solidago canadensis L. aerial part, and 2 more compounds were synthesized according to previously published methods. The study of the antimicrobial activity of compounds of these classes is an urgent problem for finding potential agents for combating MDR.

Aim. Studying of the antimicrobial activity of the isolated and synthesized substances in an individual form against Staphylococcus aureus, Escherichia coli and Candida albicans.

Materials and methods. To test the antimicrobial activity, substances of 34 compounds were used, which were obtained as a result of previous research, the structure of which were established using NMR spectroscopy and high-resolution mass spectrometry. The antifungal and antibacterial activity of the compounds were determined through the micromethod of two-fold serial dilutions in liquid nutrient medium in 96-well plates in duplicate. Screening for antimicrobial activity was carried out against reference (type) strains of Staphylococcus aureus ATCC 6538-P, Escherichia coli ATCC 25922, Candida albicans NCTC 885-653.

Results and discussion. In the group of flavonoids and O-, C-glycosides, the antifungal activity of all studied compounds did not differ significantly, but it should be noted that the antibacterial activity of apigenin C-glycosides and isoflavonoid O-glycosides was slightly greater in comparison to O-glycosides of flavonols. The greatest antimicrobial activity among the group of chalcones was shown directly by the chalcones themselves – chalcone, 2’, 4’-dihydroxychalcone, and 2’-hydroxy-4’-methoxychalcone. Among the dihydrochalcones, the highest antimicrobial activity was found for 2‘, 4’-dihydroxyhydrochalcone, which was comparable in magnitude to the antimicrobial activity of the chalcones themselves. An interesting feature of dihydrochalcones is that methylation of phenolic hydroxyl groups in the 2‘ and 4’ positions decreases the antimicrobial activity. The antimicrobial activity of 9,10-dihydrophenanthrenes, as in the case of dihydrochalcones, depended on the number of methoxy groups in the molecule. The lowest MIC values were exhibited by 4,7-dihydroxy-2,3-dimethoxy-9,10-dihydrophenanthrene containing only two methoxy groups. For bibenzyls, an inverse dependence of antimicrobial activity on the number of methoxy groups was observed – the best activity among bibenzyls against the studied strains was shown by 1-(3-hydroxyphenyl)-2-(3-hydroxy-4,5-dimethoxyphenyl)ethane, which contains two methoxy groups in its structure.

Conclusion. Polyphenolic secondary metabolites of plant origin belonging to the studied groups: flavonoids and O-, C-glycosides, chalcones, 9,10-dihydrophenanthrenes and bibenzyls did not show significant antimicrobial activity against the studied strains of microorganisms – S. aureus (6538 EP ATCC), E. coli (25922 ATCC) and C. albicans (885-653 NCTC). Despite this fact, a certain variation in antimicrobial activity was revealed depending on the structure of the tested substances.

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