In-vitro antimicrobial activity of essential oils of Tasmania

ABSTRACT Thirteen commercial Tasmanian essential oils were evaluated for their antimicrobial activity against 14 human pathogens and cosmetic contaminants including Enterococcus hirae, Kocuria rhizophila, Staphylococcus epidermidis, Propionibacterium acnes, Staphylococcus aureus, Escherichia coli, Klebsiella aerogenes, Klebsiella pneumoniae, Pluralibacter gergoviae, Pseudomonas fluorescens, Burkholderia cepacia, Pseudomonas putida, Aspergillus brasiliensis, and Aspergillus fumigatus. The antimicrobial activities of various essential oils were evaluated using the AlamarBlue Cell Viability Assay, covering a testing concentration range from 3.125 to 800 µg/mL. Essential oils were deemed active if their minimum inhibitory concentration (MIC) value was less than or equal to 800 µg/mL. The essential oils of Rosemary (Rosmarinus officinalis ct. α-pinene), Parsley Herb (Petroselinum crispum), and Bitter Fennels (Foeniculum vulgare) demonstrated significant growth inhibitory effects on one microorganism (P. fluorescens) within an MIC value of ≤ 800 µg/mL. Big Badja Gum (Eucalyptus badjensis), Blue Gum (Eucalyptus globulus), Peppermint (Mentha piperita), and Lavender (Lavandula angustifolia) essential oils inhibited the growth of two different microorganisms. Southern Rosalina (Melaleuca ericifolia), Parsley Seed (Petroselinum crispum), Smoky Tea Tree (Leptospermum glaucescens), and Kunzea (Kunzea ambigua) essential oils exhibited an MIC value of less than or equal to 800 µg/mL against 4, 5, 6, and 8 microorganisms respectively. Notably, Coastal Tea Tree (Leptospermum laevigatum) essential oil displayed the most profound antimicrobial activity, inhibiting 11 out of 15 microbial strains within an MIC range of 50–800 µg/mL. The results of the gas chromatography analysis showed that the coastal tea tree essential oil was composed primarily of monoterpenes, with smaller amounts of sesquiterpenes and their oxygenated derivatives. 35 Compounds were identified, representing 95.50% of the compounds in the coastal tea tree essential oil. The main constituents of this essential oil were α-pinene (34.83%), followed by α- and β-eudesmols (10.21% total), and limonene (9.56%).