Lyme disease is the most common vector-borne disease in the US and Europe. Although the current recommended Lyme antibiotic treatment is effective for the majority of Lyme disease patients, about 10-20% of patients continue to suffer from persisting symptoms. There have been various anecdotal reports on the use of herbal extracts for treating patients with persisting symptoms with varying degree of improvements. However, it is unclear whether the effect of the herb products is due to their direct antimicrobial activity or their effect on host immune system. In the present study, we investigated the antimicrobial effects of 12 commonly used botanical medicines and three other natural antimicrobial agents for potential anti-Borrelia burgdorferi activity in vitro. Among them, 7 natural product extracts at 1% were found to have good activity against the stationary phase B. burgdorferi culture compared to the control antibiotics doxycycline and cefuroxime. These active botanicals include Cryptolepis sanguinolenta, Juglans nigra (Black walnut), Polygonum cuspidatum (Japanese knotweed), Artemisia annua (Sweet wormwood), Uncaria tomentosa (Cat's claw), Cistus incanus, and Scutellaria baicalensis (Chinese skullcap). In contrast, Stevia rebaudiana, Andrographis paniculata, Grapefruit seed extract, colloidal silver, monolaurin, and antimicrobial peptide LL37 had little or no activity against stationary phase B. burgdorferi. The minimum inhibitory concentration (MIC) values of Artemisia annua, Juglans nigra, and Uncaria tomentosa were quite high for growing B. burgdorferi, despite their strong activity against the non-growing stationary phase B. burgdorferi. On the other hand, the top two active herbs, Cryptolepis sanguinolenta and Polygonum cuspidatum, showed strong activity against both growing B. burgdorferi (MIC = 0.03-0.06% and 0.25-0.5%, respectively) and non-growing stationary phase B. burgdorferi. In subculture studies, only 1% Cryptolepis sanguinolenta extract caused complete eradication, while doxycycline and cefuroxime and other active herbs could not eradicate B. burgdorferi stationary phase cells as many spirochetes were visible after 21-day subculture. Further studies are needed to identify the active constituents of the effective botanicals and evaluate their combinations for more effective eradication of B. burgdorferi in vitro and in vivo. The implications of these findings for improving treatment of persistent Lyme disease are discussed.

Human babesiosis is a CDC reportable disease in the United States and is recognized as an emerging health risk in multiple parts of the world. The current treatment for human babesiosis is suboptimal due to treatment failures and unwanted side effects. Although Babesia duncani was first described almost 30 years ago, further research is needed to elucidate its pathogenesis and clarify optimal treatment regimens. Here, we screened a panel of herbal medicines and identified Cryptolepis sanguinolenta, Artemisia annua, Scutellaria baicalensis, Alchornea cordifolia, and Polygonum cuspidatum to have good in vitro inhibitory activity against B. duncani in the hamster erythrocyte model. Furthermore, we found their potential bioactive compounds, cryptolepine, artemisinin, artesunate, artemether, and baicalein, to have good activity against B. duncani, with IC50 values of 3.4 μM, 14 μM, 7.4 μM, 7.8 μM, and 12 μM, respectively, which are comparable or lower than that of the currently used drugs quinine (10 μM) and clindamycin (37 μM). B. duncani treated with cryptolepine and quinine at their respective 1×, 2×, 4× and 8× IC50 values, and by artemether at 8× IC50 for three days could not regrow in subculture. Additionally, Cryptolepis sanguinolenta 90% ethanol extract also exhibited no regrowth after 6 days of subculture at doses of 2×, 4×, and 8× IC50 values. Our results indicate that some botanical medicines and their active constituents have potent activity against B. duncani in vitro and may be further explored for more effective treatment of babesiosis.

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Bartonella henselae is a Gram-negative, facultative intracellular bacterium which is the causative agent of cat scratch disease. In humans, infections with B. henselae can result in acute or chronic systemic infections with various clinical symptoms including local skin lesions, malaise, aches, chills, lymphadenopathy, endocarditis, or meningoencephalitis. The current treatment for Bartonella infections with antibiotics such as doxycycline and rifampin is not always effective presumably due to bacterial persistence. There have been various anecdotal reports of herbal extracts used for treating patients with persistent Bartonella infections but their activity on B. henselae is unknown. To test the potential antimicrobial activity of botanical or herbal medicines and develop better therapies for persistent Bartonella infections, in this study, we screened an herbal product collection against stationary phase B. henselae in vitro using SYBR Green I/ propidium iodide (PI) viability assay. These herbal medicines were selected by the fact that they are commonly used to treat Lyme and co-infections by patients and herbalists, and as a follow-up to our recent study where these herbs were tested against B. burgdorferi. We identified five herbal product extracts that had high activity against stationary phase B. henselae at 0.5% (v/v), including Cryptolepis sanguinolenta, Juglans nigra, Polygonum cuspidatum, Scutellaria baicalensis, and Scutellaria barbata. Among them, Cryptolepis sanguinolenta, Juglans nigra, and Polygonum cuspidatum could eradicate all stationary phase B. henselae cells within 7 days at 0.25% (v/v) in drug exposure time-kill assay, whereas Scutellaria baicalensis and Scutellaria barbata showed relatively poor activity. The minimum inhibitory concentration (MIC) determination of these top hits indicated they were not only active against stationary phase non-growing B. henselae but also had good activity against log phase growing B. henselae. Our findings may help to develop more effective treatments for persistent Bartonella infections.