The antimicrobial activity of origanum oil, basil oil, chamomile blue oil, tea tree oil and thyme oil against Gram-positive bacterial strains

Abstract

The potential antimicrobial activity of five essential oils was investigated against 21 Gram-positive bacteria. The bacterial strains employed in the study were wild strains isolated from food, water and clinical samples, derived from the strain collection of the Food Microbiology Unit and the Clinical Microbiology Laboratory of the University Hospital (Ioannina, Greece). All essential oils were obtained from Sigma-Aldrich (Germany); origanum oil (W282812), basil oil (W211907), chamomile blue oil (W227307), tea tree oil (W390208) and thyme oil (W306509) were tested against methicillin-resistant Staphylococcus aureus (n=7), methicillin-resistant Staphylococcus epidermidis (n=1), vancomycin-resistant Enterococcus faecium (n=2), Streptococcus pyogenes (n=1) resistant to erythromycin and clindamycin and susceptible strains of Streptococcus pyogenes (n=3), Streptococcus agalactiae (n=1), Listeria monocytogenes (n=5) and Listeria innocua (n=1) using the broth macrodilution method. Susceptibility testing to antibiotics was performed using the Bauer-Kirby method and the VITEK II system (BioMerieux). Carvacrol and thymol (Origanum oil), thymol, linalool and p-cymene (Thyme oil), terpine-4-ol and p-cymene (Tea tree oil), methyl chavicol (Basil oil) were the main components of the tested oils. Origanum oil and Thyme oil produced the strongest antimicrobial effect against all tested strains, while Tea Tree oil and Basil oil, were active to a smaller extend. Chamomile blue oil exhibited no antimicrobial properties at all. Higher inhibitory capacity was observed in the oils containing phenolic components (carvacrol and thymol). The MIC values for the tested strains ranged from 0.063 to 1% (v/v) for Origanum and Thyme oils, from 0.25 to 2% (v/v) for Tea Tree oil and from 0.25 to >4%(v/v) for Basil oil.