ANTIMICROBIAL PROPERTIES AND PHYTOCHEMICAL COMPOSITION OF SOLANUM NIGRUM COMPLEX (BLACK NIGHT SHADE)

Abstract

Solanum nigrum complex is a group of plants used as indigenous vegetables and also a source of traditional medicine in Kenya and other parts of the world. There are many species in the S. nigrum complex which include Solanum villosum, Solanum scabrum, and Solanum nigrum among others. This study determined the antibacterial properties, antifungal properties and phytochemical composition of some species in the S. nigrum complex. Samples were collected from Eldoret, Kisumu, Kakamega, and Bungoma. The plants were dried in dark room and then ground. Crude extracts were prepared from the plants using methanol. The antifungal and antibacterial properties were performed using the samples. The fungi used were Fusarium culmorum, Fusarium avenaceum and Fusarium moniliforme. The bacterial species used were Staphylococcus aureus, Salmonella typhi, Pseudomonas aureginosa, Proteus mirabilis, Shigella spp, Pseudomonas syringae, Escherichia coli and Bacillus subtilis. Minimum inhibition concentration (MIC) of the samples against active microbes was determined. Phytochemical composition of the extracts was analysed. T –test was used to analyse the significance of the activity indexes of the extracts against the different groups of the microbes. The samples collected were found to belong to the species S. nigrum, S. scabrum and S. villosum which all belong to the S. nigrum complex. The samples showed a considerable antibacterial and antifungal activity against the tested microbes. The highest antibacterial activity was 29.00 mm which was shown by sample KO4L (Bungoma less bitter) which belongs to S. villosum species; when tested against S. aureus. The antibacterial and antifungal activity was dose dependent with MIC values as low as 0.09g/ml exhibited by sample K06L against all tested bacteria. The antimicrobial activity was associated with the wide array of phytochemical compounds seen in the samples that included tannins, saponins, flavonoids, steroids, terpenes, phenolic compounds, and cardiac glycosides. A pure crystal isolated from sample K06L of the S. nigrum Mill species also exhibited a considerable level of antimicrobial activity with the highest activity index of 14.00 mm observed against S. typhi. It was concluded that the S. nigrum complex is rich in many phytochemical compounds like saponins, flavonoids, steroids, glycosides, terpenoids among others which make the plant useful in inhibition of many microbes. It can also be used in treatment of plant fungal infections and also act as a food preservative. Further research on the plants was therefore recommended in order to come up with more beneficial application of S. nigrum complex in the medical field for improvement of human health. iv