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

5.1.6 Plant extract dilutions that displayed antibacterial activity
The undiluted plant extracts of Bulbine frutescens, Leonotis leonurus, Melianthus
major & Zantedeschia aethiopica were serially diluted in the microtitre plate assay to
obtain the MIC’s of the different plant extracts. Table 9a displays the dilutions where
the MIC values were obtained for the specific plant extracts.
Twenty-one bacterial strains represented by two Gram-positive bacteria
(Staphylococcus aureus & methicillin-resistant Staphylococcus aureus) and three
Gram-negative bacteria (Pseudomonas aeruginosa, Acinetobacter baumanii &
Klebsiella pneumoniae) were used for assessing the antibacterial activity of plant
extracts in the microtitre plate assay.
The undiluted extract concentrations were different for each medicinal plant extract
following resuspension of the extract residues with solvent. The extracts of M. major
displayed the highest undiluted concentrations in comparison to the extracts of the
other plants (Table 5). Therefore the dilutions in Table 9a represent different
concentrations of the plant extracts where the MIC values (Table 9b) were obtained.
Table 9a indicates to what extent the plant extracts were diluted to display an
inhibition of the bacteria in the microtitre plate assay. The dilutions in Table 9a
correlate with the MIC values (mg/ml) in Table 9b. The specific plant extract dilutions
in Table 9a serve as a point of reference for the visible observation of MIC’s of plant
extracts.
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