| Summary: | Thesis (M.Sc. (Microbiology)) -- University of Limpopo, 2020 === The aim of the study was to isolate and characterise the antibacterial and antioxidant
compounds from the leaf extracts of the two mistletoes (Viscum rotundifolium and
Tapinanthus oleifolius) and to determine the synergistic effects of the plants with
their hosts (Mystroxylon aethiopicum and Dichrostachys cinerea). The leaves of the
selected plants were collected, dried and ground into fine powder. The powdered
plant leaves were extracted using n-hexane, ethyl acetate, acetone, methanol and
water. The qualitative phytochemical analysis was done using standard chemical
tests and thin layer chromatography. The total phenolic, tannin and flavonoid content
were estimated using spectrophotometric methods. The qualitative antioxidant
activity was determined using 2, 2-Diphenyl-1-pycrylhydryzyl (DPPH) free radical
scavenging assay on thin layer chromatography and quantitative antioxidant activity
was determined using colorimetric DPPH assay and ferric reducing power assay.
The antibacterial activity of extracts was tested against S. aureus, E. faecalis, E. coli
and P. aeruginosa using bioautography and serial broth micro-dilution assay. The
cytotoxic effects of the plant extracts were determined using cell viability assay. The
active compounds were extracted using serial exhaustive extraction and isolated
using the bioassay-guided fractionation and then purified using thin layer
chromatography and open column chromatography. The pure compound was
identified using the NMR and mass spectroscopy. Methanol was the best extractant
with the highest percentage yield. The distinct fluorescing compounds were
observed on the CEF and EMW mobile phase. The non-fluorescing compounds
detected with vanallin-sulphuric acid spray reagent showed that V. rotundifolium, T.
oleifolius and D. cinerea have more polar compounds while M. aethiopicum have
more non-polar compounds. All the plants revealed the presence of terpenoids,
flavonoids, phlobatannin, tannins steroids and cardiac-glycosides and the absence of
alkaloids and saponins. The n-hexane extract of T. oleifolius was significantly high in
flavonoid content (34.801±0.798 mgQE/g of extract) and tannin content
(15.367±0.320 mgGAE/g of extract) whereas the ethyl acetate extract of M.
aethiopicum was high in phenolic content (893.210±3.016 mgGAE/g of extract). The
results indicate that the compounds that exhibit antioxidant activity are non-polar to
polar, which was confirmed by quantitative tests. M. aethiopicum showed activity
against all tested bacteria while V. rotundifolium only had activity against E. faecalis
whereas T. oleifolius and D. cinerea did not have any activity. The quantitative
antibacterial test confirmed the activity of the plant extracts where the MIC values
ranged from 0.04-2.5 mg/mL. The combination of V. rotundifolium and M.
aethiopicum (n-hexane, ethyl acetate and acetone extracts) and T. oleifolius and D.
cinerea (n-hexane, acetone and methanol extracts) showed synergistic effects in
inhibiting the growth of S. aureus whereas the methanol extract of T. oleifolius and
D. cinerea showed antagonistic effects in inhibiting the growth of all tested bacteria.
The cell viability assay indicated that acetone extracts of all plants were non-toxic on
the human liver (C3A) cells. M. aethiopicum was selected for isolation and
purification of bioactive compounds. The bioassay-guided fractionation led to the
isolation of oleanolic acid acetate. This study demonstrated that the selected plants
have antibacterial potential that is ascribed to the phytochemicals present. Further
studies including in vivo assays are needed in order to support their use in traditional
medicine === National Research Foundation (NRF)
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