Synergistic interactions of selected medicinal plants traditionally used to treat meningitis

The antibacterial and antifungal activities of aqueous, methanol and acetone extracts of the leaves of Geranium incanum, Mangifera indica, Bidens pilosa, Ricinus communis, Carica papaya and fruit pulp of Adansonia digitata as well as activity of their combined preparation were evaluated against selected meningitis causing pathogens. The microorganisms under study were methicillin and oxacillin resistant Staphylococcus aureus (ATCC 43300), Pseudomonas aeruginosa (ATCC 27853), Salmonella typhimurium (ATCC 49416), Escherichia coli (ATCC 35218), Candida albicans (ATCC 10231) and Cryptococcus neoformans (clinical strain). The screening of antimicrobial activities were assessed using an agar well diffusion technique for the different plant extractions. The individual and combined plant extracts that demonstrated antimicrobial effects were further studied using the INT microtitre plate technique to determine the minimum inhibitory concentration. The sum of fractional inhibitory concentration indices were calculated and used to assess the type of antimicrobial interaction. The medicinal plants exerted antimicrobial effects independently and in combination on the bacterial and fungal organisms under study. The antimicrobial activities depended on the test organism and extracting solvents used. In the combination studies, the medicinal plants under study were combined in the ratio of 1:1. Antimicrobial interactions ranging from synergistic to antagonistic effects were noted. Methanol extracts of combinations B. pilosa: M. indica, R. communins: M. indica and C. papaya: M. indica had synergistic effects against P. aeruginosa. On the other hand, aqueous extracts of a mixture of C. papaya: B. pilosa exerted synergistic effects on E. coli and S. typhimurium. Acetone extracts of a mixture of A. digitata: G. incanum, G. incanum: M. indica as well as methanol extract of the combination of C. papaya: G. incanum exhibited synergistic effects against C. albicans. The aqueous extract combination of G. incanum: M. indica displayed the most noteworthy synergistic activity against C. neoformans. In addition, aqueous extracts of the combinations of A. digitata: B. pilosa and R. communis: G. incanum exhibited synergistic effects against C. neoformans. The results validate the traditional healing practices which utilise combinations of different species of plants for treatment of predisposing factors of meningitis