Identification of Essential Oils with Strong Activity against Stationary Phase .

Lyme disease is the most common vector borne-disease in the United States (US). While the majority of the Lyme disease patients can be cured with 2⁻4 weeks antibiotic treatment, about 10⁻20% of patients continue to suffer from persisting symptoms. While the cause of this condition is unclear, persistent infection was proposed as one possibility. It has recently been shown that develops dormant persisters in stationary phase cultures that are not killed by the current Lyme antibiotics, and there is interest in identifying novel drug candidates that more effectively kill such forms. We previously identified some highly active essential oils with excellent activity against biofilm and stationary phase Here, we screened another 35 essential oils and found 10 essential oils ( L. bulbs, Lindl. berries, L. seeds, var. Bruno grass, (T. Nees) Engl. resin, Buch.-Ham. ex Sm. flowers, L. wood, L. leaves, (Lour.) Pers. fruits, Hook. leaves) and the active component of cinnamon bark cinnamaldehyde (CA) at a low concentration of 0.1% have strong activity against stationary phase . At a lower concentration of 0.05%, essential oils of L. bulbs, Lindl. berries, var. Bruno grass and CA still exhibited strong activity against the stationary phase . CA also showed strong activity against replicating , with a MIC of 0.02% (or 0.2 μg/mL). In subculture studies, the top five essential oil hits L. bulbs, Lindl. berries, (T. Nees) Engl. resin, Buch.-Ham. ex Sm. flowers, and (Lour.) Pers. fruits completely eradicated all stationary phase cells at 0.1%, while var. Bruno grass, Hook. leaves, L. wood, L. seeds, and L. leaves failed to do so as shown by visible spirochetal growth after 21-day subculture. At concentration of 0.05%, only L. bulbs essential oil and CA sterilized the stationary phase culture, as shown by no regrowth during subculture, while Lindl. berries, (T. Nees) Engl. resin, Buch.-Ham. ex Sm. flowers and (Lour.) Pers. fruits essential oils all had visible growth during subculture. Future studies are needed to determine if these highly active essential oils could eradicate persistent infection in vivo.