Probiotics are defined by the FAO/WHO as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host”. So far there are only two strains of yeast documented as probiotic: Saccharomyces cerevisiae boulardii, which is used as an anti-diarrheal treatment and a specific strain of Saccharomyces cerevisiae.
Note: at the end of the baking process, yeast is deactivated. This means that in bread, yeast is not consumed alive and cannot have probiotic actions in the human organism.