Living microorganisms are widely used for several therapeutic purposes and their beneficial effects as biotherapeutic agents are well known. While certain strains of lactic acid bacteria and bifidobacteria are used as probiotics in pharmaceutical preparations, feed additives and so-called functional foods yeasts also possess some medicinal efficiency.

The beneficial properties of strains of some Saccharomyces spp are well documented (Rodrigues et al. 1996). In addition to their nutritive value (e.g. provision of vitamins of the B group), probiotic yeasts are generally resistant to gastrointestinal passage and are resistant to most antibiotics. Yeast preparations have also been successfully applied, in combination with antibiotics, to treat Clostridium difficile -related diarrhoea commonly known as antibiotic associated diarrhoea. Probiotic Saccharomyces spp may also help to re-establish a normal gut function after long term antibiotic therapy (McFarland et al., 1994).

Some Saccharomyces spp also have a protective effect, and specific activities, against various enteric pathogens. Saccharomyces spp stimulate sIgA production and the phagocytic system of gnotobiotic mice (Rodrigues et al., 2000). These probiotic yeasts may also have efficacy in the prevention of Traveler's diarrhoea.

Strains of so-called Saccharomyces boulardii, taxonomic status some what unclear since recent work suggests it is a subspecies of Saccharomyces cerevisiae, are regarded as the most prominent representatives of probiotic yeasts within the community of biotherapeutic S. cerevisiae strains. Today, a considerable number of pharmaceutical preparations (capsules, powders, tablets, pellets) containing probiotic yeasts ( Saccharomyces spp ) cells are commercially available, and are marketed mainly via pharmacies and health stores.

We prefer to use the term biotherapeutic agent rather than probiotic because it denotes a microorganism having therapeutic properties (McFarland, 1996).

Biotherapeutic agents, as with probiotics, must be given in sufficient concentration to exert therapeutic properties, remain stable and viable before use and survive in the intestinal ecosystem of the host to exert their therapeutic properties.