study was done for: 1. Isolation and identification of Saccharomyces cerevisiae var boulardii from different fresh and dried local fruit in Erbil city. 2. Determination the inhibitory activity of the isolated yeasts against pathogenic bacteria (in vitro). 3. Study the effect of physiological factors on survival of the isolated yeasts . 4. Determination the effect of some environmental factors (pH, temperature, incubation period and aeration) on producing inhibitory substances. 5. Study the effect of isolated yeast strain on survival of the experimental animals infected with pathogenic...