A PRELIMINARY PHYTOCHEMICAL STUDY OF DIPLORHYNCHUS CONDYLOCARPON, HOLARRHENA PUBESCENS, PSIDIUM GUAJAVA, SCLEROCARYA BIRREA, STEGANOTAENIA ARALICEA, TRICHILIA EMETICA AND VERNONIA GLABRA USED FOR THE TREATMENT OF DIARRHOEA BY TRADITIONAL HEALERS IN MALAWI

Abstract

Diarrhoea is one of the common ailments amongst children as well as adults in Malawi. It is mainly caused by bacterial pathogens. These bacterial diarrhogenic problems are treatable using antibiotics available at healthcare facilities. However, healthcare facilities are not readily accessible to majority of rural and urban poor population such that the majority rely on traditional medicine and medicinal plants for health problems such as diarrhoea. Ethnobotanical survey on medicinal plants traditionally used for diarrhoea problems have been carried out. However, phytochemical screening and antibacterial activity of these plants is not done. Therefore, selected seven medicinal plants (Diplorhynchus condylocarpon, Guajava psidium, Holarrhena pubescens, Sclerocarya birrea, Steganotaenia aralicea, Trichilia emetica and Vernonia glabra), used locally to treat diarrhoea in Malawi were investigated for their classes of phytochemicals and in vitro antibacterial activity. The presence of alkaloids, saponins, terpenoids, flavonoids and tannins was determined in the leaves, stem and root barks of the plant species using standard phytochemical methods. Plant species were extracted using methanol, ethyl acetate, and dichloromethane by soxhlation, and water using cold extraction. The yields, phytochemical composition and antibacterial activity of the resulting crude extracts were determined and compared. Growth inhibition, using agar disc diffusion method was determined against five gram-negative bacterial entero-pathogens, Salmonella typhi, S. typhimurium, S. enteritidis, Shigella boydii and S. flexneri. The plant species whose crude extracts gave high yields and phytochemical composition, and exhibited significantly high efficacies were selected for further studies. Minimum Inhibitory Concentrations (MIC) were determined for methanolic crude extracts from root and stem barks of D. condylocarpon and H. pubescens. Yields, thin layer chromatography (TLC) and UV spectra of crude extracts of alkaloids, saponins, terpenoids and flavonoids from the two plant species were also determined and analysed. Phytochemical composition, yield and antibacterial activity of the crude extracts varied significantly with plant species and the extracting solvent (p < 0.001). Methanol was found to be the most effective extracting solvent system such that its crude extracts exhibited the largest number of phytochemicals, and gave the highest yields of the three organic extracting solvents. The yields of crude extracts varied from 3.06  0.12 % to 13.26  0.19 %. Extracts of all the plant species except T. emetica were active against at least three pathogens tested, and the mean inhibition diameters of the active extracts varied from 8.3  0.2 mm to 16.6  0.2 mm. However, methanolic crude extracts of root and stem barks of D. condylocarpon and H. pubescens were the most active against the tested bacterial strains. The strain, S. flexneri, was the most susceptible while S. typhimurium was the most resistant pathogen. Alkaloids, saponins and tannins, which are some of the classes of phytochemicals associated with antimicrobial properties in medicinal plants, were observed in the aqueous extracts of the selected plants. However, alkaloids were predominant class of phytochemicals in all four extracting solvents. Only aqueous extracts of root and stem barks of D. condylocarpon and H. pubescens were active against the tested bacterial strains. Traditional healers commonly use aqueous extracts to treat their patients. Therefore, presence of these phytochemicals in aqueous extracts supports the use of these plants for therapeutically purposes. Hence, aqueous extracts of root and stem barks of D. condylocarpon and H. pubescens should be promoted. However, proper methods of harvesting these plants should be adhered to in order to ensure sustainability of the species. The MIC of crude extracts of D. condylocarpon and H. pubescens ranged from 0.80 to 25.00 mg/ml and 0.20 to 15.00 mg/ml, respectively, indicating that crude extracts of H. pubescens were more active than those of D. condylocarpon. The yields of alkaloids, saponins, flavonoids and terpenoids in D. condylocarpon and H. pubescens were significantly different (p <0.05). The crude saponin extracts of D. condylocarpon and H. pubescens showed at least three spots on the TLC plates using butanol: ethanol: water (5:3:1), revealing that these plants contain more than one type of saponins. Further separation and isolation techniques needs to be explored in order to determine identities of the bioactive agents.