Bangladeshi Medicinal Plants: Ethnopharmacology, Phytochemistry and Anti-Staphylococcal Activity

Antibacterial resistance is a major concern. Due to its new resistance mechanism, it is spreading and emerging globally and thereby threatening the treatment of common infectious diseases. There is no doubt to develop new antibiotic from natural sources to tackle antimicrobial resistance. This study involves, (1) ethnopharmacological survey in Bangladesh and (2) bioassay directed phytochemical investigation to explore antibacterial compounds against MRSA. In 2016, an ethnopharmacological survey conducted in Bangladesh led to the recommendation of 71 medicinal plants by 71 Ayurvedic/Unani practitioners, 21 Ayurvedic patients and 35 local inhabitants for the treatment of infectious diseases. Based on the review of literature, data analysis and ease of availability of the plants, 18 plants were initially selected and collected from Bangladesh. After initial antibacterial screening of 18 plants, five plants (MIC 32-512 μg/ml) were chosen based on potential antibacterial activity. These are (Zingiber montanum, Uraria picta, Diospyros malabarica, Cynometra namiflora, Swertia chirayita). Extensive phytochemical work using different chromatographic (VLC, Coloumn chromatography, SPE, TLC, PTLC) and spectroscopic (NMR, Mass spectromentry, IR) techniques on five Bangladeshi medicinal plants led to the isolation and identification of 25 compounds. Eight terpenes (zerumbol, zerumbone, buddledone A, germacrone, furanodienone, (-) borneol, camphor and 8(17), 12-labdadiene-15, 16-dial) were isolated from Zingiber montanum with the MIC (32- >128 μg/ml). Eugenol and steriods were isolated from Uraria picta (MIC 64- >128 μg/ml). Lupane type triterpenoids (Lupeol, botulin, betulinaldehyde, betulone and messagenin) were isolated and identified from Diospyros malabarica with the MIC (64- >128 μg/ml) while pentacyclic triterpene (glutinol, glutinone), simple phenolic (ethyl 4-ethoxybenzoate) and steroids were isolated from Cynometra ramiflora with MIC (64- >128 μg/ml). A series of xanthones (swerchirin, swertiaperenin, belidifolin and decussatin) were identified from Swertia chirayita with MIC (>128 μg/ml). Among these compounds, 4-ethoxybenzoate, messagenin were identified as new natural compounds. In terms of activity, 8(17), 12-labdadiene-15, 16-dial (32 μg/ml against ATCC 5941) and zerumbol (32 μg/ml against EMRSA 15) showed potential antibacterial activity.