ANTIMICROBIAL PROPERTIES OF BLACK NIGHT SHADE (SOLANUM NIGRUM) GROWN IN THE RIFT VALLEY, WESTERN AND NYANZA REGIONS OF KENYA

Abstract

Solanum nigrum complex comprises of plant species that belong to Solanum section Solanum used as indigenous leafy vegetables in Kenya. The S. nigrum complex species have been used traditionally as medicine. Many species make up the S. nigrum complex. Purpose of this study was to determine the antimicrobial properties of the methanol extracts of S. nigrum complex on bacteria and fungi. The study sought to identify the species grown in Rift valley, Nyanza and Western regions of Kenya while at the same time determining the phytochemical composition of the species. Collected plant materials from the various ecological zones in Kenya were slowly dried, ground and extracted with methanol. Evaluation for antimicrobial activity using eight bacterial and three fungal species was done and the significant difference in activity of the species in the different zones established using analysis of variance done by Statistical Package for Social Sciences. Gram-negative bacteria of Escherichia coli, Klebsiella pneumonia, Proteus vulgaris, Shigella flexneri, Pseudomonas aureginosa, and Salmonella typhimurium and gram-positive bacteria of Staphylococcus aureus and Bacillus cereus were used. The fungal species included Fusarium moniliforme, Fusarium oxysporum, and Fusarium graminearum. Phytochemical analysis of the sample extracts was carried out with tannins, saponins, alkaloids, flavonoids, cardiac glycosides, phlobatanins, phenolic compounds, terpenoids and steroids being found as the main phytochemicals. The minimum inhibitory concentration of the extracts against each microorganism was determined. Results on geographical distribution of Solanum species showed that S. nigrum, S. scabrum and S. villosum were available in Western Kenya, while S. villosum, S. nigrum and S. scabrum were common in Nyanza Kenya. S. villosum, S. scrabrum and S. nigrum were common in Rift Valley region. Only S. nigrum from Kisii, Nyamira and Busia, S. scabrum from Iten, Nyando, and Busia, and S. villosum from Nyamira showed antibacterial activity against all the gram-positive bacteria and P. vulgaris, S. flexneri, S. typhimurium, K. pneumoniae, and E. coli for gram negatives. Maximum inhibition zone of 27.33mm against B. cereus was recorded in extracts from both S. scabrum Busia and S. villosum Nyamira. However, S. flexneri was resistant to S. nigrum Busia, S. nigrum Nyamira, S. scabrum Iten and S. scabrum Nyando. E. coli was resistant to S. scabrum Iten and S. scabrum Busia. Findings on Minimum Inhibitory Concentration revealed that the results of the test extracts ranged from 0.40-0.90 mg/mL. All the extracts except S. villosum Nyamira recorded the lowest minimum inhibitory concentration of 0.40mg/mL for B. cereus. In addition, all the test extracts except S. scabrum Iten, which showed 0.60 mg/ml, had highest minimum inhibitory concentration of 0.80 mg/ml for S. nigrum Kisii, S. nigrum Busia, and S. villosum Nyamira, while 0.90 mg/ml for S. scabrum Busia, S. scabrum Nyando, and S. nigrum Nyamira for K. pneumoniae. At a p-value of 0.05 the S. nigrum species were showed to have a significant difference in their antimicrobial activity with a p-value of less than 0.05. The study has shown that S. nigrum complex has antimicrobial activity against bacteria and could lead to its usage as food with health benefits and source of nutraceuticals.