Identification of essential oils with activity against stationary phase Staphylococcus aureus

Abstract

Staphylococcus aureus is the most dominant human pathogen, responsible for a variety of chronic and severe infections. There is mounting evidence that persisters are associated with treatment failure and relapse of persistent infections. While some essential oils were reported to have antimicrobial activity against growing S. aureus, activity of essential oils against the non-growing stationary phase S. aureus enriched in persisters has not been investigated. In this study, we evaluated the activity of 143 essential oils against stationary phase S. aureus and identified 39 essential oils (Cinnamon bark, Oregano, Thyme white, Bandit \"Thieves\", Lemongrass (Cymbopogon flexuosus), Sandalwood oil, Health shield, Allspice, Amyris, Palmarosa, Cinnamon leaf, Clove bud, Citronella, Geranium bourbon, Marjoram, Peppermint, Lemongrass (Cymbopogon citratus), Cornmint, Elemi, Ho wood, Head ease, Lemon eucalyptus, Litsea cubeba, Myrrh, Parsley seed, Coriander oil, Dillweed, Hyssop, Neroli, Rosewood oil, Tea tree, Cajeput, Glove bud, Lavender, Sleep tight, Vetiver, Palo santo, Sage oil, Yarrow) at 0.5% concentration, 10 essential oils (Cinnamon bark, Oregano, Thyme white, Bandit \"Thieves\", Lemongrass (Cymbopogon flexuosus), Sandalwood oil, Health shield, Allspice, Amyris, Palmarosa) at 0.25% concentration, and 7 essential oils (Cinnamon bark, Oregano, Thyme white, Lemongrass (Cymbopogon flexuosus), Allspice, Amyris, Palmarosa) at 0.125% concentration to have high activity against stationary phase S. aureus with no visible growth on agar plates after five-day exposure. Among the 10 essential oils which showed high activity at 0.25% concentration, 9 (Cinnamon bark, Oregano, Thyme white, Bandit \"Thieves\", Lemongrass (Cymbopogon flexuosus), Health shield, Allspice, Palmarosa, Amyris) showed higher activity than the known persister drug tosufloxacin, while the other one (Sandalwood oil) was found to be active at a higher concentration. In Oregano essential oil drug combination studies with clinical antibiotics, Oregano plus quinolone drugs (tosufloxacin, levofloxacin, ciprofloxacin) and rifampin completely eradicated all stationary phase S. aureus cells, but had no apparent enhancement for linezolid, vancomycin, sulfamethoxazole, trimethoprim, azithromycin and gentamicin. Our findings may facilitate development of more effective treatment for persistent S. aureus infections.