Isolation, Purification, Identification, Synthesis, and Kinetics of Activity of the Anticandidal Component of Allium Sativum, and a Hypothesis for Its Mode of Action

SUMMARY

Aqueous extracts of bulbs of garlic (Allium sativum L). were fungicidal for 39 of 41 recent clinical isolates of Candida albicans at 68 μg total dry weight of crude extract per ml of 2% (w/v) malt extract broth in standing culture; the remaining two isolates gave variable or moderate growth at 68 μg/ml. In shake culture in a chemically defined medium which maintained yeast morphology, the crude extract was fungistatic between 50 and 300 μg/ml and fungicidal above 400 μg/ml. Gradual loss of anticandidal activity occurred when crude extract was stored at 37 C before being assayed; loss of activity was proportional to duration of heat treatment. Activity was stable in acid and unstable in base. Column chromatography of garlic extract using Sephadex G-10 gel implicated an anticandidal component having a molecular weight of less than 700. These characteristics correspond with those of the known antibacterial principle of garlic, allicin (diallyl thiosulfinate). Allicin was chemically synthesized. Extraction procedures which select for allicin were performed on aqueous extracts of garlic, and on anticandidal fractions obtained from rechromatography on a G-10 column. The anticandidal components in aqueous extracts of garlic, in G-10 fractions, and in solutions of synthetic allicin had similar chemical and biological characteristics. Anticandidal activity of all preparations was destroyed by thiols such as L-cysteine or glutathione. Activity was also destroyed by the reducing agent dithioerythritol, but not by the disulfide cystine. Thin layer chromatography produced a spot, common to extracts of garlic and to synthesized allicin, that inhibited growth of C. albicans on biochromatograms. This spot was absent from extracts of the L-cysteine-aqueous garlic reaction mixture, and these extracts lacked anticandidal activity. Biochromatograms of an extract of aqueous garlic suggest that allicin is the major anticandidal component, and that other thiosulfinates in garlic extracts may have some anticandidal activity. Anticandidal activity was only slightly antagonized by serum concentrations of 5 and 10%. A hypothesis is proposed which explains the basis for the anticandidal activity of allicin.