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extract. The starting concentration in the first well after the dilution was 50 mg/ml.
Micro plates were covered with lids and incubated at 37 ºC overnight. 40 µl of the
0.2% solution of P-Iodonitrotetrazolium violet (Sigma) (0.2 mg/ml) reagent was used
to indicate the presence of uninhibited bacterial growth (a pink/purple colour) or the
inhibition (colourless) of bacterial growth in each well. The lowest concentration of
the crude plant extract that inhibited bacterial growth was taken as the MIC (Mathabe
et al., 2006).
2.6 PHYTOCHEMICAL SCREENING
2.6.1 Alkaloids
Dried plant material (1 g) was extracted with 5 ml ethanol and evaporated to
dryness. The residue was heated in a boiling water bath with 5 ml HCl (2M). It was
then cooled and filtered. The filtrate was divided into two equal portions, of which
one was treated with a few drops of Mayer’s reagent and the other portion treated
with the same amount of Dragendorff’s reagent. The samples were observed for
turbidity or precipitation, which is an indication of the presence of alkaloids
(Harborne, 1973).
2.6.2 Flavonoids
Dried plant material (1 g) was extracted with 5 ml ethanol and evaporated to
dryness. The residue was treated with a few drops of concentrated HCl and 0.5 g
magnesium turnings. The presence of flavonoids was indicated by the development
of a pink or magenta-red colour within three minutes (Harborne, 1973).
2.6.3 Saponins
Plant material (2.5 g) was extracted with boiling water (5 ml) and then allowed to
cool. The extract was then shaken vigorously to froth and allowed to stand for 20
minutes. The presence of saponins is determined by the presence of froth (Brain &
Turner 1975).
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