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

microtitre plate assay. Following prolonged incubation periods (90 – 120 minutes) of
the three bacteria only slight or no colour change were visible in comparison with the
other bacteria (Figure 6). Based on these findings it was decided to substitute the
distilled water diluent in the microtitre plate assay with an enriched medium, Mueller
Hinton (MH) broth. Although using MH broth as an alternative diluent, the
absorbance values of these bacteria obtained with the microtitre plate reader still
gave high rates of inconsistency in comparison to the other test bacteria.
The three bacteria were not compatible with the microtitre plate assay and its
subsequent spectrophotometric microtitre plate analysis in this study. The other
bacteria S. aureus, P. aeruginosa and K. pneumoniae were successfully reduced by
INT tested on the same microtitre plates (Figure 6).
S. pyogenes E. feacalis S. aureus Controls P. mirabilis P. aeruginosa K. pneumoniae Controls
FIGURE 6
Lack of INT reductions by the three bacteria
4.4.2 Agar dilution assay
The strains of the three bacteria, E. feacalis, S. pyogenes & P. mirabilis, that
produced inconsistent absorbance readings with the microtitre plate assay were
tested with an adapted agar dilution assay. The agar dilution assay allowed for the
determination of the MIC’s on agar plates prepared with plant extracts at different
concentrations (Boswell et al., 2001; Andrews, 2004).
The agar plates containing plant extracts and a 36-pin multipoint inoculator (Mast
diagnostics, UK) device, served as the basis for antibacterial activity testing of the
plant extracts. The agar dilution assay using a multipoint inoculator, worked well in
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