an investigation into the antibacterial activities of medicinal plants ...

aethiopica inhibited a maximum of 10 bacterial strains whereas the aqueous extract
inhibited the minimum of 7 bacterial strains for the Z. aethiopica extracts.
The results in Table 9b indicate that the methanol extract of all the plants inhibited
the highest number of bacterial strains; therefore it displayed the highest antibacterial
activity. Rabe & Van Staden, 1997 and Vlachos et al., 1996 reported similar findings
on the high antibacterial activity displayed by the methanol extract in comparison to
other extracts.
The aqueous/water extracts of the plants inhibited the lowest number of bacterial
strains in comparison to the other extracts for each plant (Table 9b). This compares
with Shale et al., 1999 that reported on the water being less effective than methanol
at extracting the active compounds from plants.
The agar dilution assay was used for screening and testing the antibacterial activity
of all plant extracts at concentrations ranging between 0.5 and 20 mg/ml against the
bacterial strains of P. mirabilis, S. pyogenes and E. feacalis (Table’s 12 & 13). Only
the bacterial strains of P. mirabilis were inhibited by the extracts. The acetone and
methanol extracts of M. major were the only extracts that displayed antibacterial
activity (Table 12).
A comparative testing of different M. major acetone extractions obtained from freshly
crushed leaves and refrigerated fresh leaves crushed the previous day displayed a
significant difference in the antibacterial activity. The acetone extract obtained from
fresh leaves crushed a day prior to extraction (kept refrigerated), failed to inhibit the
P. mirabilis strains (Figure 14). The test indicated that the antibacterial activity was
lost or absent after the overnight refrigeration of the freshly crushed leaves. The
active compounds of M. major leaves may have been oxidised or undergone
chemical alterations after overnight refrigeration, resulting in a loss of activity.
Besides the different plant extracts, the traditional preparations of the plants were
tested for antibacterial activity as these preparations are used traditionally by the
indigenous people (Van Wyk et al., 1997). In the microtitre plate assay the B.
frutescens infusion and the Z. aethiopica decoction inhibited 8 of the 21 bacterial
strains. The L. leonurus and M. major decoctions inhibited 20 of the 21 bacterial
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