| Summary: | Dissertation submitted in fulfilment for the requirements of the Degree of
Master of Technology in Biomedical Technology, Durban University of Technology, 2012. === Introduction
Medicinal plants have been used for centuries as remedies for human diseases
because they contain components of therapeutic value. Recently, the acceptance of
traditional medicine as an alternative form of health care and the development of
microbial resistance to the available antibiotics have led scientists to investigate the
antimicrobial activity of medicinal plants
Aim
The aim of this study was to investigate the antimicrobial activity of extracts
obtained from medicinal plants used in traditional medicine. A comparative study
was carried out on the antimicrobial properties of extracts obtained by two different
methods in order to choose that which extracts the most effective antimicrobial
compounds.
Methodology
The plants used in this study Artemisia afra, Erythrina lysistemon and Psidium
guajava were harvested from the Silverglen Nature Reserve (Chatsworth) early in the
morning (8 a.m.). The leaves of A. afra and P. guajava extracts and the bark of E.
Lysistemon were used to prepare the extracts. All plant extracts were prepared
according to modified method of the German Homeopathic Pharmacopoea. Two
solvents, water and 60 percent ethanol were used to extract the antibacterial
compounds from plant material.
The extracts were then assessed for their antibacterial activity against Staphylococcus
aureus, Pseudomonas aeruginosa and Escherichia coli. The effect of the plant
extracts on these bacteria was determined by the disk diffusion test, which was used
as the screening test. Positive results were further subjected to the minimum
inhibitory concentration and minimum bactericidal concentration assays. Tubes that
showed no turbidity were then sub-cultured onto non-selective plates. Bacterial
sensitivity testing was carried out in accordance with modified Kirby-Bauer
Antimicrobial Sensitivity Test.
An attempt was made to identify some antibacterial compounds using Thin Layer
Chromatography and High Pressure Liquid Chromatography.
Results
None of the gram negative organisms were inhibited by Artemisia afra, Erythrina
cafra and Psidium guajava. Only the ethanol extracts of all three plants were able to
inhibit Staphylococcus aureus but not Escherichia coli and Pseudomonas
auruginosa. None of the test organisms were inhibited by the aqueous extracts of all
three plants used in this study. In the screening test, the zones of inhibition for
ethanol extracts against Staphylococcus aureus ranged from 3mm – 7mm. The
minimum inhibitory concentration ranged from 16.67 percent – 83.3 percent
inhibition depending on the dilution of the extract.
Quercetin and Catechin were identified as some of the antibacterial compounds
present in the leaves of Psidium guajava. These two compounds were not identified
on Erythrina lysistemon and Artemisia afra.
Conclusion
The results obtained in this study have proven that Artemisia afra, Erythrina cafra
and Psidium guajava ethanol extracts contain antibacterial substances. The ethanol
extracts of all plants in this study inhibited the growth of Staphylococcus aureus but
had no effect on the gram negative bacteria. Aqueous plant did not inhibit the growth
of any bacteria in this study. This study has also shown that antibacterial effect of
these extracts may be considerably enhanced in traditional treatment if traditional
healers can include ethanol as one of the extraction solvents. The results obtained in
this study might be considered sufficient for further studies aimed at isolating and
identifying the active compounds and evaluating possible synergism of antimicrobial
activity among these extracts. Investigations on toxicity of these extracts should also
be carried out.
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