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The work presented in this thesis involves scientific investigation of 25 plant species, used in traditional medicine of Ghana to treat skin disease and/or to treat antimicrobial (viral, bacterial or protozoan) infections which were identified through an ethnobotanical survey. It also involves antimicrobial screening, matrix-assisted laser desorption/ionization time of-flight mass spectrometry (MALDI-ToF-MS) for the identification of antibacterial compounds of low molecular mass in aqueous extracts of Cryptolepis sanguinolenta roots and Alchornea cordifolia leaves. The thesis consists of 3 related studies. In the first study, 25 plant species were collected through an ethnobotanical survey in Ghana. Extracts of the plant species (chloroform, ethanol and aqueous) were prepared and agar well diffusion tests, MIC's and MBC's were used to investigate antibacterial activity with special interest in antimethicillin- resistant Staphylococcus aureus (MRSA) activity as the bacteria has become a problem worldwide and the need for novel sources of agents against MRSA. Extracts of 13 plant species inhibited the growth of one or more of the following bacteria: MRSA, methicillin-sensitive Staph aureus (MSSA), Streptococcus pyogenes, Escherichia coli, Pseudomonas aeruginosa and Proteus vulgaris. Extracts from I1 of these 13 plant species also inhibited the growth of three or more of 14 additional clinical isolates of MRSA. Aqueous extracts of Alchornea cordifolia were active against all 21 bacterial strains tested and showed the highest levels of anti-bacterial activity overall with MIC values against MRSA in the range of 1.6-3.1 mg ml-1 and MBC values in the range of 6.3-12.5 mg ml's. The presence of antibacterial activity in extracts of Elaeophorbia drupifera, Solanum verbascifolium and the ethanol extract of Rauwolfia vomitoria are reported for the first time. Extracts from Alchornea cordifolia, also used to treat wounds, had the widest spectrum of anti-bacterial activity. The second study describes sample preparation methods for the analysis of low molecular mass antibacterial compounds in aqueous root extract of C. sanguinolenta leading to the rapid identification of cryptolepine using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS). Antibacterial evaluation of cryptolepine on Staph aureus and MRSA showed that concentration range 0.02-0.03 mg ml"' (MIC) of the compound presents bacteriostatic effects on the bacteria. Eleven synthetic combinational derivatives based on the quindoline (cryptolepine) structure were also tested against Staph aureus and MRSA. MIC values of the derivatives were ranging from 0.1-2 mg ml-1 against the bacteria tested. Chlorocryptolepine derivative had the lowest MIC value of 0.01 mg ml"' and represents a possible antibacterial agent for further development. In the third study, based on the antibacterial activity, aqueous leaf extract of Alchornea cordifolia was further investigated against 32 clinical isolates of MRSA. Inhibition zone diameters range from 18-30 mm against the isolates. MIC and MBC values ranging from 1.6-3.1 mg ml-1 and 6.3-12.5 mg ml'' of the plant extract were found against the MRSA isolates. Phytochemical screening of the aqueous leaf extract of the plant showed the presence of alkaloids, saponins and tannins. MALDI-ToF-MS analysis showed peaks at m/z 170 and 207 which corresponded to gallic acid and alchornine respectively. |
