Antimicrobial activity of Hyssopus officinalis L. subsp. aristatus (Godr.) Nyman (Lamiaceae) essential oils from Montenegro and Serbia

In this study, antimicrobial activity of essential oils extracted from the aerial flowering parts (herbs) of Hyssopus officinalis subsp. aristatus (Godr.) Nyman (Lamiaceae) collected from five different locations in Montenegro, or purchased in Serbia, were investigated. In addition, their antibacterial activity in combination with antibiotics was studied. The antimicrobial activity against selected standard bacterial and yeast strains was investigated using the broth microdilution method. Two standard antibiotics were used for comparison: the aminoglycoside antibiotic amikacin and the cephalosporin antibiotic ceftriaxone. The antimicrobial activity of the essential oil-amikacin combination was investigated using the checkerboard assay. The main components of the essential oils were 1,8-cineole, cis-pinocamphone, β-pinene and limonene in varying quantities. Most of the tested essential oils showed no significant antimicrobial activity. However, an essential oil rich in cis-pinocamphone showed moderate activity against both Staphylococcus aureus and Escherichia coli (MIC = 400 µg/mL). The overall effect of the essential oils and antibiotic combinations against E. coli or S. aureus ranged from additive (FICI = 0.625) to indifferent (FICI = 1.5), depending on the source of the essential oil.