Antimicrobial and antioxidant activity of the vegetative and reproductive organs of Robinia pseudoacacia

This study was aimed at investigating the antimicrobial and antioxidant activity of ethanol extracts obtained from the leaves, seeds and sheaths of Robinia pseudoacacia. Total phenolic content (TPC, Folin-Ciocalteu method), antioxidant activity (trolox equivalent antioxidant capacity (TEAC) assay) and antimicrobial activity (agar disk diffusion method and broth dilution method) of the vegetative and reproductive organs of R. pseudoacacia were determined. The highest content of polyphenols (expressed as gallic acid equivalents, GAE) was found in the extract of R. pseudoacacia leaves (266.7 mu g GAE mL(-1) extract) followed by the extract of the seeds (232.2 tg GAE mL(-1) extract). HPLC analysis showed the presence of catechin (0.925 mu g mL(-1)), rutin (0.831 mu g mL(-1)), resveratrol (0.664 mu g mL(-1)) and quercetin (0.456 mu g mL(-1)) in the leaf extract, and catechin (0.127 mu g mL(-1)), epicatechin (0.239 mu g mL(-1)) and rutin (0.231 mu g mL(-1)) in the seed extract. The results showed that the studied extracts exhibited a selective antimicrobial effect directed against Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli) bacterial strains. The combination leaf extract/antibiotic had the highest synergistic effect when compared to combinations with seed and sheath extracts. The same extract with penicillin G, kanamycin and rifampin had highest synergetic effect against methicillin-resistant S. aureus strain (MRSA), a strain that has gained great interest of microbiologists within the past decades. The chemical characterization of ethanol extracts from the vegetative and reproductive organs of R. pseudoacacia, the synergistic effects of certain antibiotics and acacia extracts and the potential to increase the antimicrobial activity of some commercial antibiotics against MRSA were investigated for the first time.