The aqueous extract of A. sativum showed the lowest inhibitory
effect on S. agalactiae both in the swab paper disc assay and determination
of MIC. This may be related to the characteristics of allicin.
Allicin is an oxygenated sulphur compound, formed when garlic
cloves are crushed. Allicin is considered to be the most potent antibacterial
agent in crushed garlic, but it is unstable, and breaks down
within 16 h at 23 °C (22). In an aqueous garlic extract, allicin was
found to decompose very quickly (22). When allicin reacts withwater,
it transforms to diallyl disulphide, which exhibits a lower level of
antimicrobial activity than allicin (23, 24). Hughes and Lawson (11)
performed tests with S. aureus and reported that pure allicin had a
MIC of 27 μg/mL compared with 900 μg/mL for diallyl disulphide.