Antimicrobial assay and phyto-chemical analysis of Solanum nigrum complex growing in Kenya

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. The main objective of this study was to determine the antimicrobial property and phytochemical composition of S. nigrum complex. Samples of S. nigrum complex were collected from Kenya. The plants were dried under the shade and then ground to a fine powder. Crude extracts were prepared from the plants using methanol and evaluated for antifungal and antibacterial activities against the fungi Fusarium culmorum, Fusarium avenaceum, Fusarium moniliforme and bacteria Staphylococcus aureus, Salmonella typhi, Pseudomonas aureginosa, Proteus mirabilis, Shigella spp., Pseudomonas syringae, Escherichia coli and Basillus subtilis. Minimum inhibition concentration (MIC) of the samples against active microbes was determined. Phytochemical composition 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, Solanum scabrum and Solanum 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 S. villosum species against S. aureus. The antibacterial and antifungal activities were dose dependent with low MIC values as such 0.09 g/ml given by S. nigrum Mill species against all eight tested bacteria. The antimicrobial activity was associated with the wide array of phytochemical compounds observed in the samples and they include tannins, saponins, flavonoids, steroids, terpenes, phenolic compounds, alkaloids and cardiac glycosides. It was concluded that the S. nigrum complex is rich in many phytochemical compounds like saponins, flavanoids, steroids, glycosides, terpenoids among others which are responsible for the antimicrobial activities of the plants. It can be used not only in treatment of plant fungal infections but also in the management of bacterial human diseases and further research is recommended.