university of kwazulu-natal faculty of science and agriculture school ...

eing incubated for 24 hours at 37°C. A volume of 40µL of 0.2mg/mL
Iodonitrotetrazolium chloride (INT, Sigma) was added to each well as indicator of
bacterial growth. INT, a colourless tetrazolium salt, is converted to a red-coloured
formazan product by actively dividing cells. The minimum inhibitory concentration
(MIC) was visually read as the lowest concentration of sample that inhibited microbial
growth, as indicated by a visible reduction in the red colour of the INT formazan. In each
assay, a negative solvent control and a positive control of the antibiotic was used.
Gentamicin (Sigma) was used as the antibacterial control and the samples were tested in
triplicate.
4.1.2 Results and discussion
The results of the Minimum Inhibitory Concentration (MIC) determinations of the four
compounds against Enterococcus faecalis and Pseudomonas aeruginosa are given in
Table 27. MIC values for the samples and the reference antibiotic, gentamicin are
reported in µg/mL.
Table 27: Antibacterial activity of compounds I to IV
Compound
Average MIC (µg/mL)
24 hours
E. faecalis P. aeruginosa
I 62.50 62.50
II 31.30 7.80
III 125.00 15.60
IV 200.00 200.00
Gentamicin 0.39 0.78
The antibacterial activity of compounds I to IV were evaluated relative to gentamicin.
The lower the MIC value, the better the antibacterial activity of the compound. Since the
MIC value for gentamicin is below 1µg/mL for both the bacterial strains tested,
compounds with MIC values below 10µg/mL were noted to be potent antibacterial agents
while compounds having MIC values between 10µg/mL and 100µg/mL were considered
to be good antibacterial agents. Compounds exhibiting MIC values between 100µg/mL
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