Phytomedicine Programme, Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, 0110, South Africa.
Current address: Department of Pharmacy and Pharmacology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, Johannesburg, 2193, South Africa.
BMC Complement Med Ther. 2020 Nov 23;20(1):358. doi: 10.1186/s12906-020-03139-4.
Diarrhoea is a major health issue in both humans and animals and may be caused by bacterial, viral and fungal infections. Previous studies highlighted excellent activity of Newtonia buchananii and N. hildebrandtii leaf extracts against bacterial and fungal organisms related to diarrhoea-causing pathogens. The aim of this study was to isolate the compound(s) responsible for antimicrobial activity and to investigate efficacy of the extracts and purified compound against bacterial biofilms.
The acetone extract of N. buchananii leaf powder was separated by solvent-solvent partitioning into eight fractions, followed by bioassay-guided fractionation for isolation of antimicrobial compounds. Antibacterial activity testing was performed using a broth microdilution assay. The cytotoxicity was evaluated against Vero cells using a colorimetric MTT assay. A crystal violet method was employed to test the inhibitory effect of acetone, methanol: dichloromethane and water (cold and hot) extracts of N. buchananii and N. hildebrandtii leaves and the purified compound on biofilm formation of Pseudomonas aeruginosa, Escherichia coli, Salmonella Typhimurium, Enterococcus faecalis, Staphylococcus aureus and Bacillus cereus.
Myricetin-3-o-rhamnoside (myricitrin) was isolated for the first time from N. buchananii. Myricitrin was active against B. cereus, E. coli and S. aureus (MIC = 62.5 μg/ml in all cases). Additionally, myricitrin had relatively low cytotoxicity with IC = 104 μg/ml. Extracts of both plant species had stronger biofilm inhibitory activity against Gram-positive than Gram-negative bacteria. The most sensitive bacterial strains were E. faecalis and S. aureus. The cold and hot water leaf extracts of N. buchananii had antibacterial activity and were relatively non-cytotoxic with selectivity index values of 1.98-11.44.
The purified compound, myricitrin, contributed to the activity of N. buchananii but it is likely that synergistic effects play a role in the antibacterial and antibiofilm efficacy of the plant extract. The cold and hot water leaf extracts of N. buchananii may be developed as potential antibacterial and antibiofilm agents in the natural treatment of gastrointestinal disorders including diarrhoea in both human and veterinary medicine.
腹泻是人类和动物的主要健康问题，可能由细菌、病毒和真菌感染引起。先前的研究强调了 Newtonia buchananii 和 N. hildebrandtii 叶提取物对与腹泻病原体相关的细菌和真菌的极好活性。本研究的目的是分离负责抗菌活性的化合物，并研究提取物和纯化化合物对细菌生物膜的功效。
用溶剂-溶剂分配法将 N. buchananii 叶粉的丙酮提取物分离成八个部分，然后进行生物测定指导的分离以分离抗菌化合物。使用肉汤微量稀释法进行抗菌活性测试。使用比色 MTT 测定法评估细胞毒性。采用结晶紫法测试 N. buchananii 和 N. hildebrandtii 叶的丙酮、甲醇：二氯甲烷和水（冷和热）提取物以及纯化化合物对铜绿假单胞菌、大肠杆菌、肠炎沙门氏菌、粪肠球菌、金黄色葡萄球菌和蜡样芽孢杆菌生物膜形成的抑制作用。
首次从 N. buchananii 中分离出杨梅素-3-O-鼠李糖苷（杨梅苷）。杨梅苷对蜡样芽孢杆菌、大肠杆菌和金黄色葡萄球菌均具有活性（所有情况下 MIC=62.5μg/ml）。此外，杨梅苷的细胞毒性相对较低，IC=104μg/ml。两种植物提取物对革兰氏阳性菌的生物膜抑制活性均强于革兰氏阴性菌。最敏感的细菌菌株是粪肠球菌和金黄色葡萄球菌。N. buchananii 的冷热水叶提取物具有抗菌活性且相对非细胞毒性，选择性指数值为 1.98-11.44。
纯化的化合物杨梅苷对 N. buchananii 的活性有贡献，但协同作用可能在植物提取物的抗菌和抗生物膜功效中起作用。N. buchananii 的冷热水叶提取物可能作为天然治疗人类和兽医胃肠道疾病（包括腹泻）的潜在抗菌和抗生物膜剂。
