Effect of Citrus Pulp on the Viability of Saccharomyces boulardii in the Presence of Enteric Pathogens †

Saccharomyces cerevisiae boulardii is frequently used as a dietary supplement to promote intestinal health and reduce the impact of growth of enteric pathogens in livestock, including cattle and swine. Citrus by-products are also fed as dietary supplements that have the additional benefit of inhibiting the growth of enteric pathogens. Previous research identified that supplementation of Saccharomyces boulardii to feed containing citrus pulp significantly reduced the average daily gain of weanling pigs challenged with Salmonella enterica, suggesting citrus pulp reduces the effectiveness of Saccharomyces boulardii. To investigate this possibility, an in vitro analysis was conducted on the activity of Saccharomyces boulardii in swine fecal microbial media supplemented with citrus pulp. Citrus pulp inclusion reduced (P < 0.01) populations of Saccharomyces boulardii within 48 h post-exposure, suggesting that this product may exhibit antifungal properties. Co-incubation of Salmonella with Saccharomyces boulardii reduced populations of both microbes; inclusion of citrus pulp did not lead to a further reduction of yeast populations in the coculture. The cell lysate from Saccharomyces boulardii was also found to provide a carbon source that was utilizable by Escherichia coli, but not Salmonella. Together, these results suggest that citrus pulp reduces the viability of Saccharomyces boulardii and that the subsequent effects of this interaction on enterics are varied. Though further research is needed to determine how citrus pulp influences the activity of Saccharomyes boulardii in vivo, these data strongly suggest caution should be exercised in providing citrus pulp to livestock being fed diets supplemented with live yeast probiotics.