and tannins in thyme; and salicin, tannin, and essential oil in willow
(18). Tannin is a compound, which has antimicrobial activity, and can
be isolated from plants by water (19), ethanol (20), and methanol
extraction (21). Thus, it is possible that antimicrobial compounds of
the herbs tested in this study can be extracted by all three solvents.
Although all herb extracts used in this study had antimicrobial effects
on S. agalactiae, the effects were dependent on the extracting solvents.
We suggest that the herb compounds responsible for antimicrobial
effects are extracted by different solvents to different degrees.
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 with water,
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.
Based on inhibition zone size and MIC value, the aqueous extract of
A. paniculata showed the highest antimicrobial activity against S.
agalactiae. This result when combined with those of our previous