| dc.description.abstract | Over the years, the potential of plants as a source of new antimicrobial substances has
been determined but is still under-explored. In Africa and most developing countries,
traditional medicine still forms the backbone of rural medicinal practice. In addition,
the emergence of new diseases and drug resistant microorganisms has highlighted an
essential role of medicinal plants as a source for new healing agents in development of
therapeutic drugs. This study aimed at determining the antibacterial and
immunomodulatory activity of Vernoa hildebrandtii, Acacia stuhlmannii (Taub) and
Moringa oleifera leaf and root-bark extracts. Crude extracts were obtained from dried
powder by single solvent maceration with ethanol and water. Bioassay-guided
procedures were used to evaluate the bioactivity of the extracts against Escherichia coli
and Staphylococcus aureus. Antibacterial activity was determined by agar diffusion
method. Elisa was used to assay for Interleukin -10 and Interferon gamma production.
In addition, (3-(4, 5-Dimethylthiazol 2-yl)-2,5-diphenyltetrazolium bromide (MTT) was
used to determine cytotoxicity. Statistical analyses were performed using one way
ANOVA followed by student t-test. Results were considered statistically significant at P
< 0.05. M. oleifera leaf water extract was the most potent fraction with the highest zone
of inhibition of 32 ± 2 mm followed by A. stuhlmannii (Taub) root-bark water extracts
with a zone of inhibition of 31 ± 2 mm. A. stuhlmannii (Taub) leaf extracts did not show
any antimicrobial activities against all the tested microorganisms. The plant extracts
exhibited a dose dependent antibacterial effect on the E. coli and S. aureus bacteria.
Human PBMCs treated with leaf and root-bark extracts showed secretion of IFN-γ with
M. oleifera root-bark alcohol extracts showing highest secretion as compared to the
controls while down regulating IL-10. The extracts significantly increased cell
proliferation in a dose-dependent manner as demonstrated by the increase in cell
viability probably due to low cytotoxicity levels. V. hildebrandtii leaf water extract had
the highest cell proliferation with a mean cytotoxic concentration (CC50) value of 42.22
µg/ml, A. stuhlmannii (Taub) leaf alcohol and Moringa oleifera leaf water extracts both
recording a CC50 value of 37.77 µg/ml. The toxicity results showed that all the extracts
except Moringa oleifera root-bark water were within the accepted cytotoxicity levels
(<CC50 20 µg/ml toxic > non-toxic). Taken together, these results confirm that M. oleifera
have antibacterial properties against E. coli and S. aureus bacteria. Further, they
demonstrate the potential of V. hildebrandtii and Acacia stuhlmannii (Taub) as new
sources of bioactive agents in the management of E. coli and S. aureus pathogens. The
findings further demonstrate for the first time, to the best of our knowledge, that V.
hildebrandtii has a very high selective potential for antibacterial activity. Further, there
was a considerable degree of immunomodulation as demonstrated by up-regulation of
IFN-γ and down-regulation of IL-10 as the plant extract concentration increased,
meaning cell mediated immune response is stimulated. | en_US |
