The microaerophilic flagellate Giardia intestinalis: Allium sativum (garlic) is an effective antigiardial

Whole garlic (Allium sativum L.) extract and some of its components were as sayed for antigiardial activity. Whole garlic extract gave an IC50 at 24 h of 0.3 mg ml(-1). Most of the components assayed were inhibitory to the org anism, especially allyl alcohol and allyl mercaptan, with IC50 values of 7 mug ml(-1) and 37 mug ml(-1) respectively. Studies with calcofluor white in dicated that whole garlic and allyl alcohol collapse the transmembrane elec trochemical membrane potential (Delta psi) of the organism, as indicated by uptake of the fluorochrome. Electron microscopy allowed the morphological changes that occur with garlic inhibition to be recorded. Both the surface topography and internal architecture of the organism changed during incubat ion with the biocides. Both whole garlic and allyl alcohol resulted in frag mentation of the disc and an overexpression of disc microribbons, internali zation of flagella, vacuole formation and an increase in distended vesicles . Allyl mercaptan, however, only gave an increase in distended vesicles, su ggesting that this biocide has a different mode of action.