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Eleven medicinal plants used by traditional healers in Machakos and Kitui District were screened, namely: Ajuga remota Benth, Aloe secundiflora Engl, Amaranthus hybridus L, Cassia didymobotrya Fes, Croton macrostachyus Del, Entada leptostachya Harms, Erythrina abyssinica DC, Harrisonia abyssinica Oliv, Schkuhria pinnata O. Ktze, Terminalia kilimandscharica Engl and Ziziphus abyssinica Hochst for potential antibacterial activity against four medically important bacterial strains, namely: Bacillus cereus ATCC 11778, Escherichia coli ATCC 25922, Micrococcus lutea ATCC 9341 and Pseudomonas aeruginosa ATCC 27853. The antibacterial activity of methanol extracts was determined as the minimum inhibitory concentration (MIC). The plant extracts were more active against Gram-positive (G+) than Gram-negative (G-) bacteria. The positive controls were streptomycin and benzylpenicillin for G- and G+ bacteria, respectively, both had a significant MIC at <1 mg/mL. The most susceptible bacteria were B. cereus, followed by M. lutea, while the most resistant bacteria were Ps. aeruginosa, followed by E. coli. The present study supports the use of these plants by the herbalists in the management of bacterial ailments. H. abyssinica and T. kilimandscharica showed the best antibacterial activity; hence these plants can be further subjected to phytochemical and pharmacological evaluation.

Direct detection of saponins in medicinal plants using Fourier Transform Infrared (FTIR) spectroscopy is reported in this paper. Crude dry plant powders were mixed with potassium bromide (KBr) powder and compressed to a thin pellet for infrared examination. FTIR spectra of the test samples showed -OH, -C=O, C-H, and C=C absorptions characteristic of oleanane triterpenoid saponins. The C-O-C absorptions indicated glycoside linkages to the sapogenins. Phytochemical analysis confirmed the presence of saponins in the tested specimens. Entada leptostachya was used as a reference sample. Dry plant powder was extracted sequentially with hexane, dichloromethane, ethyl acetate and methanol. FTIR spectra of the reference sample powder and its organic solvent extracts showed characteristic saponin absorption peaks. These results indicated that direct detection of saponins in medicinal plants was possible by infrared analysis. Lengthy exhaustive chemical analyses necessary for detection of saponins could be avoided.