ANTIBACTERIAL ACTIVITIES, ALLELOPATHIC EFFECTS AND PHYTOCHEMICAL COMPOSITION OF Centella asiatica, Dichondra repens AND Hydrocotyle mannii

Abstract

Indigenous communities depend almost entirely on herbal remedies as the main source of their demands for primary healthcare. Medicinal plants like Centella asiatica, Dichondra repens and Hydrocotyle mannii have been used by residents of Nandi County for treating ear infections and abdominal ailments. More people died from antibiotic resistant bacteria than of HIV and AIDS in 2019. This is due to antibiotics being used in improper, irregular, and unreasonable ways. Approximately 60% of children are estimated to have experienced at least one episode of Otitis media (ear infections) by 7 years. In addition to having medicinal properties, C. asiatica, D. repens and H. mannii are weeds that may possess allelopathic properties. Crop losses caused by weeds are believed to be greater than those caused by insects, pests, and diseases. This study determined the antibacterial activities, allelopathic effects and phytochemical composition of C. asiatica, D. repens and H mannii. The plant leaves were collected, shade dried followed by extraction using water, diethyl ether, ethanol and ethyl acetate. Extracts were tested against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus to determine antibacterial activities as well on maize, oats, rice, sorghum and wheat seeds to establish their allelopathic effects. Susceptibility test was done by disc diffusion using six mm discs with desired extract concentrations (100 to 10-3 ) with Ciprofloxacin as a positive control. Clear zones around the discs were measured as inhibition zone diameters. Allelopathic effects was tested by placing 10 surface sterilized seeds in each Petri dish. Twenty-four millilitres of the test extracts was used with distilled water as a positive control. The test extracts showed significant inhibitory effect against the test bacterial strains as well as test seeds which was evident from inhibition zone diameters and the plumule and radicle lengths. MANOVA determined that all the main factors and interactions with the exceptions of the interaction between plant type and bacteria species and the interaction between the concentrations, plant type and bacteria species used had a statistically significant effect on the inhibition zone diameters as well as plumule and radicle lengths at P ≤ 0.05. Alkaloids, coumarins, flavonoids, glycosides, phenols, quinones, saponins, steroids, tannins and terpenoids were screened with only glycosides absent in any of the test plant extracts. This study concludes that the phytochemicals present in the extracts of the plants under investigation were responsible for the antibacterial and allelopathic activities of the plants to varying degrees. Water can be used for optimal yield of crude extracts. The plants had allelopathic effect on test plants and can be recommended as weed control agents. Medicinal plants have a promising future as most of them have not yet been investigated for their hidden potential which could be decisive in the development of newer and more effective antimicrobials as well as in controlling growth of other plant species.