Staphylococcus aureus is a very common bacteria, responsible for a variety of chronic and severe infections. If infections caused by S. aureus are not effectively treated, high mortality in some patients could occur. Although antibiotic resistance is a major problem in treatment of infections caused by S. aureus, drug-tolerant persisters such as small colony variants (SCVs) are demonstrated to be significant contributors of chronic persistent infections and recurrent infections. Persisters are non-growing or slow growing antibiotic-tolerant bacterial cells that are able to revert to growing forms under appropriate conditions and cause relapse or persistent infections with symptoms. Clinically, infections caused by S. aureus such as soft tissue infections, endocarditis, osteomyelitis, prosthetic joint infections, and biofilm-related infections on indwelling device is difficult to cure with the current antibiotics, which are mainly active against the growing bacteria but have poor activity against the non-growing persisters.
Essential oils are concentrated volatile liquids extracted from plants. They are widely used in food processing, aromatherapy and also in medical therapy especially with recent concerns on anti-bacteria activity. Many studies reveal that essential oils have antibacterial activity against both Gram-negative and Gram-positive bacteria. In addition, various compositions of essential oils including eugenol, carvacrol and thymol have been demonstrated to be active against different bacterial species . While some essential oils were reported to have antimicrobial activity against growing S. aureus, activity of essential oils against the stationary phase S. aureus enriched in persisters has not been investigated before.
This was the first study of a large collection of 143 essential oils for activity against stationary phase S. aureus where it was identified several promising essential oils. The top hits are Oregano, Cinnamon bark, Thyme white, Lemongrass (Cymbopogon flexuosus), Bandit “Thieves”, Sandalwood oil, Health shield, Allspice, Amyris, Palmarosa. Meanwhile, it was found in drug combination study with essential oil (Oregano) and antibiotics that some potent combinations such as Oregano plus quinolones or rifampin could effectively eradicate S. aureus persisters in vitro.
These highly active essential oils form the basis for future studies to identify the active antimicrobial components, and this also suggests you can use these oils to clean surfaces.