Antimicrobial and phytochemical analyses of selected medicinal plants from Kenya

Abstract

Medicinal plants play an important role in the health of millions of people. The four plants E. burtii, E. sacleuxii, Ageratum conyzoides and Ximenia caffra were selected on the basis of available ethnomedicinal information. The crude extracts from various parts of these plants tested against four bacteria species; three Gram positive (namely Bacillus subtilis, Staphylococcus aureus and a methicillin – resistant strain of Staphylococcus aureus, MRSA) and two Gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa), using the Kirby-bauer disc diffusion technique recommended by the Clinical and Laboratory Standards Institute (CLSI). All the crude plant extracts showed antimicrobial activities against the Gram positive bacteria, including MRSA. The stem and root bark extracts of E. burtii and E. sacleuxii showed the highest activities with growth inhibition zones ranging from 8 mm at 0.050 mg/ml to 14 mm at 0.0250 mg/ml. Of these extracts the stem bark of E. sacleuxii was further tested. The extract fractions as well as five pure compounds isolated from this plant were further tested. Among the pure compounds tested, 2,3–dehydrokievitone showed the highest activity with growth inhibition zones ranging from 10 mm at the lowest concentration of 0.00312 mg/ml to 27 mm at the highest concentration of 0.0050 mg/ml against the Gram positive bacteria Bacillus subtilis, 8 mm at 0.00250 mg/ml to 18 mm at 0.0050 mg/ml, against Staphylococcus aureus,9 mm at 0.00312 mg/ml to 24 mm at 0.0050 mg/ml, against the methicillin – resistant strain of Staphylococcus aureus,it also showed activity against the Gram negative bacteria with growth inhibition zones ranging from 8 mm at 0.00625 mg/ml to 10 mm at 0.00250 mg/ml for E. coli and 8 mm at 0.00625 mg/ml to 14 mm at 0.0050 mg/ml against P. aeruginosa. The compound 3'–prenylbiochamin A also showed activity with growth inhibition zones of between 10 mm at 0.00625 mg/ml to 21 mm at 0.005 mg/ml against E. coli, 12 mm at 0.00625 mg/ml to 19 mm at 0.0050 mg/ml against S. aureus, 9 mm at 0.00312 mg/ml to 28 mm at 0.0050 mg/ml against B. subtilis, 9 mm at 0.00625 mg/ml to 14 mm at 0.0050 mg/ml for P. aeruginosa, growth inhibition zones of between 8 mm at 0.00312 mg/ml and 28 mm at 0.0050 mg/ml were noted against the methicillin – resistant strain of S. aureus,MRSA. All the crude plant extracts of E.burtii, A. conyzoides, X. caffra and E. sacleuxii and the Column Chromatography fractions, were tested for their antifungal activities against the fungi species Aspergillus flavus, Penicillium digitatum and Fusarium oxysporum. All of these extracts showed no antifungal activity against the fungi species tested. Isolation and identification of the pure compounds from the extracts of E.burtii, A.conyzoides and X. caffra are recommended, however the toxicities of the active extracts and pure compounds should be assessed in order to establish their practical applications.