Synergistic antibacterial interaction between Melissa officinalis extracts and antibiotics

Synergism between water, ethanol and ethyl acetate extract of Melissa officinalis and five commonly used antibiotics (streptomycin, chloramphenicol, tetracycline, amoxicillin, rifamycine) were investigated by disc diffusion method in relation to antibiotic-susceptible and antibiotic resistant human-pathogenic bacteria. The total phenol content in the extracts were determined by Folin-Ciocalteau`s method while the flavonoid concentration by aluminium chloride method. The extracts, at least with one antibiotic, showed synergistic interaction. Depending on the species of bacteria, the zones of inhibition in extract/antibiotic plates were in the range of 0.5 – 11.5 mm wider than in controls. The certain extract/antibiotic combinations exhibited significant results against antibiotic resistant bacteria (the inhibition zones were 711mm wider than in controls). The ethanol and ethyl acetate extracts showed better synergistic capacity than water extract. The least susceptible bacteria to extract/antibiotic combinations were Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis. The highest amount of total phenols was measured in water extract while the highest amount of flavonoids had ethyl acetate extract.