HERBAL PRODUCTS AND ESSENTIAL OILS WITH HIGH ACTIVITY AGAINST STATIONARY PHASE BARTONELLA HENSELAE
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Date
2020-04-24
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Johns Hopkins University
Abstract
Bartonella henselae is a Gram-negative bacterium which is the causative agent of cat scratch disease. Humans infection with B. henselae can result in acute or chronic systemic infections. The current antibiotic therapy to treat Bartonella infections is not very effective, presumably due to the bacterial persistence. This phenomenon gives rise to the importance of identifying more active drugs targeting bacterial persister cells to develop more effective therapies.
Herbal products and essential oils are plant extracts containing organic chemical compounds. Many botanical extracts and essential oil components have been documented to have antimicrobial activities. Nowadays it is important to study botanical products with potential antimicrobial activity, especially with the great concern about increasing antibiotic resistance.
In this study, we performed a high-throughput screening of two collections of herbal products and essential oils for active hits against stationary phase B. henselae in vitro. The primary screen was conducted using a SYBR Green I/propidium iodide (PI) viability assay, followed by colony forming unit (CFU) assay throughout a seven-day drug exposure to confirm top hits. We successfully identified 3 herbal product extracts that had high activity against stationary phase B. henselae at 0.25% (v/v), derived from Cryptolepis sanguinolenta, Juglans nigra, and Polygonum cuspidatum. In addition, we identified 32 essential oils that had high activity against stationary phase B. henselae, including four essential oils extracted from Citrus plants, three from Origanum, three from Cinnamomum, two from Pelargonium, and two from Melaleuca, as well as frankincense, ylang-ylang, fir needle, mountain savory (winter), citronella, spearmint, elemi, vetiver, clove bud, allspice, and cedarwood essential oils. The time-kill assay showed 13 active hits could eradicate all stationary phase B. henselae in seven days at 0.032% (v/v). Two active ingredients, carvacrol and cinnamaldehyde, of oregano and cinnamon bark essential oils, respectively, were shown to be very active such that they were able to eradicate all the B. henselae cells even at ≤ 0.01% (v/v). The minimum inhibitory concentration (MIC) determination of these active hits indicated they also had good activity against log phase growing B. henselae. These findings may have implications for developing more effective treatments for persistent Bartonella infections.
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Keywords
Bartonella henselae, herbal product, essential oil, bacterial persistence