Chemical composition and biological activities of essential oil from flowers of Psidium guajava (Myrtaceae)

Abstract Xylella fastidiosa is a plant-pathogenic bacterium that lives inside host xylem vessels, where it forms biofilm which is believed to be responsible for disrupting the passage of water and nutrients. Pectobacterium carotovorum is a Gram-negative plant-specific bacterium that causes not only soft rot in various plant hosts, but also blackleg in potato by plant cell wall degradation. Chagas disease, which is caused by Trypanosoma cruzi, has been commonly treated with nifurtimox and benzonidazole, two drugs that cause several side effects. As a result, the use of natural products for treating bacterial and neglected diseases has increased in recent years and plants have become a promising alternative to developing new medicines. Therefore, this study aimed to determine, for the first time, the chemical composition of essential oil from Psidium guajava flowers (PG-EO) and to evaluate its in vitro anti-Xylella fastidiosa, anti-Pectobacterium carotovorum, anti-Trypanosoma cruzi and cytotoxic activities. PG-EO was obtained by hydrodistillation in a Clevenger apparatus while its chemical composition was determined by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Major compounds identified in PG-EO were α-cadinol (37.8%), β-caryophyllene (12.2%), nerolidol (9.1%), α-selinene (8.8%), β-selinene (7.4%) and caryophyllene oxide (7.2%). Results showed that the PG-EO had strong trypanocidal activity against the trypomastigote forms of Trypanosoma cruzi (IC50 = 14.6 μg/mL), promising antibacterial activity against X. fastidiosa (MIC = 12.5 μg/mL) and P. carotovorum (MIC = 62.5 μg/mL), and moderate cytotoxicity against LLCMK2 adherent epithelial cells in the concentration range (CC50 = 250.5 μg/mL). In short, the PG-EO can be considered a new source of bioactive compounds for the development of pesticides and trypanocide drugs.

摘要 苛养木杆菌（Xylella fastidiosa）是一种寄生于宿主木质部导管内的植物病原细菌，可在其中形成生物膜，据信该生物膜会阻断水分与养分的运输通路。胡萝卜软腐果胶杆菌（Pectobacterium carotovorum）是一类革兰氏阴性植物专性寄生细菌，不仅可诱发多种宿主植物产生软腐病，还可通过降解植物细胞壁引发马铃薯黑胫病。由克氏锥虫（Trypanosoma cruzi）引起的恰加斯病，临床常规治疗药物为硝呋替莫（nifurtimox）与苯硝唑（benzonidazole），但这两种药物均会引发多种不良反应。近年来，利用天然产物治疗细菌性疾病与被忽视热带病的研究热度逐渐升高，植物也成为开发新型药物的极具潜力的替代来源。有鉴于此，本研究首次对番石榴花精油（PG-EO，即Psidium guajava flowers essential oil）的化学成分进行分析，并体外评价其抗苛养木杆菌、抗胡萝卜软腐果胶杆菌、抗克氏锥虫及细胞毒性活性。PG-EO通过克利夫伦杰蒸馏装置（Clevenger apparatus）采用水蒸馏法提取，其化学成分借助气相色谱-火焰离子化检测器（GC-FID）与气相色谱-质谱联用仪（GC-MS）完成鉴定。PG-EO中的主要成分为α-荜澄茄醇（α-cadinol，37.8%）、β-石竹烯（β-caryophyllene，12.2%）、橙花叔醇（nerolidol，9.1%）、α-芹子烯（α-selinene，8.8%）、β-芹子烯（β-selinene，7.4%）与石竹烯氧化物（caryophyllene oxide，7.2%）。实验结果表明，PG-EO对克氏锥虫锥鞭毛体（trypomastigote）具有较强的杀锥虫活性（半数抑制浓度IC₅₀=14.6 μg/mL），对苛养木杆菌（最低抑菌浓度MIC=12.5 μg/mL）与胡萝卜软腐果胶杆菌（MIC=62.5 μg/mL）展现出良好的抗菌活性，且在实验浓度范围内对LLCMK₂贴壁上皮细胞（LLCMK2 adherent epithelial cells）具有中等细胞毒性（半数细胞毒性浓度CC₅₀=250.5 μg/mL）。综上，番石榴花精油可作为开发农药与杀锥虫药物的新型生物活性化合物来源。