INHIBITORY ACTIVITY OF SACCHAROMYCES YEASTS ON THE ADHESION OF ENTAMOEBA-HISTOLYTICA TROPHOZOITES TO HUMAN ERYTHROCYTES IN-VITRO

Adhesion to target cells represents the first step in infection by Ent amoeba histolytica. Binding of axenic amoeba (HMI strain) to human red cells in vitro was employed as a model of the adhesion process. The i nfluence of precontact of trophozoites with suspensions of live Saccha romyces boulardii yeasts, their fractions (membranes and yeast-content supernatant before and after filtration to eliminate the membrane) or yeast culture medium before and after fermentation was investigated. N-Acetylgalactosamine (GalNAC) was employed as the reference inhibitor y sugar. The percentage of amoebae bearing red cells after pretreatmen t of amoebae with the various suspensions and derivates was determined . Adhesion was also evaluated by scanning electron microscopy (SEM). P retreatment of amoebae with the live yeast suspension led to a signifi cant reduction in the percentage of adhesion [32% vs 70% in the phosph ate-buffered saline (PBS) control]. Reduced adhesion was also observed with the filtered and unfiltered supernatant of the yeast suspension homogenate [32% and 34%, respectively, vs 69% in the PBS control], yea st culture medium at the end of fermentation [49% vs 76% in the PBS co ntrol] and GalNAC [32% vs 72% in the PBS control]. SEM showed a decrea se in the number of amoebae bearing red cells and a reduction in the n umber of red cells adhering to amoebae. We conclude that substances pr oduced by the yeasts compete with red cells for adhesion sites on amoe bae.