Lyme disease, which is caused by Borrelia burgdorferi bacteria, is the most common vector borne-disease in the United States with about 300,000 cases a year. While the majority of the Lyme disease patients can be cured with the standard 2–4 weeks antibiotic monotherapy with doxycycline or amoxicillin or cefuroxime, about 36% of patients continue to suffer from persisting symptoms of fatigue, joint, or musculoskeletal pain, and neuropsychiatric symptoms, even six months after taking the standard antibiotic therapy. These latter patients suffer from a poorly understood condition, called ‘post-treatment Lyme disease’ syndrome. A research team led by Professor Ying Zhang from Hopkins Bloomberg School of Public Health previously identified several essential oils — oils that are pressed from plants or their fruits and contain the plant’s main fragrance, or ‘essence’ — with excellent activity against dormant and slow-growing ‘persister’ forms of Borrelia burgdorferi. In a new study, published in the journal Antibiotics, they screened another 35 essential oils and found 10 new highly active oils (garlic, allspice, cumin, palmarosa, myrrh, hydacheim, amyris, thyme white, Litsea cubeba, lemon eucalyptus).
The cause of post-treatment Lyme disease syndrome isn’t known. But it is known that cultures of Borrelia burgdorferi can enter a so-called stationary phase in which many of the cells divide slowly or not at all.
The slow-dividing or dormant cells are ‘persister’ cells, which can form naturally under nutrient starvation or stress conditions, and are more resistant to antibiotics.
Some researchers have sought other drugs or medicinal compounds that can kill persister Borrelia burgdorferi in the hope that these compounds can be used to treat people with persistent Lyme symptoms.
In a 2017 study, Professor Zhang and co-authors found that essential oils from oregano, cinnamon bark, clove buds, citronella and wintergreen killed stationary phase Borrelia burgdorferi even more potently than daptomycin, the champion among tested pharmaceuticals.
In the new study, they extended their lab-dish testing to include 35 other essential oils, and found 10 that show significant killing activity against stationary phase Lyme bacteria cultures at concentrations of just one part per thousand.
At this concentration, five of these oils — derived respectively from garlic bulbs, allspice berries, myrrh trees, hydacheim (spiked ginger lily) blossoms and Litsea cubeba (may chang) fruit — successfully killed all stationary phase Borrelia burgdorferi in their culture dishes in seven days, so no bacteria grew back in 21 days.
Oils from thyme leaves, cumin seeds and amyris wood also performed well, as did cinnamaldehyde, the fragrant main ingredient of cinnamon bark oil.
“We found that these essential oils were even better at killing the persister forms of Borrelia burgdorferi than standard Lyme antibiotics,” Professor Zhang said.
Lab-dish tests such as these represent an early stage of research, but the team hopes in the near future to continue with tests in live animals, including tests in mouse models of persistent Lyme infection. If those tests go well and the effective doses seem safe, the scientists expect to organize initial tests in humans.
“At this stage these essential oils look very promising as candidate treatments for persistent Lyme infection, but ultimately we need properly designed clinical trials,” Professor Zhang said.
Jie Feng et al. 2018. Identification of Essential Oils with Strong Activity against Stationary Phase Borrelia burgdorferi. Antibiotics 7 (4): 89; doi: 10.3390/antibiotics7040089