89
YEAST PROBIOTICS VARY IN THEIR POTENTIAL TO BIND TO GRAM POSITIVE OR GRAM NEGATIVE BACTERIA
Probiotics are widely utilized in the livestock industry to improve health and overall productivity. Despite the extensive amount of research performed on examining the mechanisms by which probiotics confer positive effects upon hosts, their use is still highly debated and are undoubtedly under characterized. The hypothesis for this study was that variations exist in the binding potential of probiotics to Gram-negative and Gram-positive bacteria. To test this hypothesis, the binding capability of five different types of live yeasts or yeast cell wall products to two Gram-negative bacteria (Salmonella typhimurium and Escherichia coli O157:H7) and three Gram-positive bacteria (Listeria monocytogenes, Clostridium perfringens, and Bifidobacterium bifidum) was determined using an adhesion assay and subsequent analysis by scanning electron microscope. The probiotics were incubated on coverslips then challenged with the array of different pathogens. To assess each probiotic’s propensity towards adhesion, extensive washings of the coverslips were done. This removal of unbound bacteria determined that any bacteria remaining resulted from direct interactions between the pathogens and the probiotics, inferring antagonistic behavior of adhesion displayed by the probiotics. Though S. typhimurium bound well to all probiotics tested (>90%, P = 0.3), E. coli O157:H7 had a preference (P = 0.003) to bind to the yeast cell wall products in comparison to live yeast. The opposite was observed for the Gram-positive bacteria tested, which exhibited an improved binding potential to live yeast (P = 0.01). A sample size of >20 yeast cells or cell wall products was analyzed. This data suggest that combining both live yeast probiotic and yeast cell product probiotic will allow for an increase in binding to different enteric bacteria. To test the binding capability of this combination mixture to colon epithelial cells, another adhesion assay was performed and prepared for analysis by fluorescent microscope (one fluorochrome labeling epithelial DNA and another staining yeast actin filaments). A sample size of >30 epithelial cells was analyzed. The data determined that no variations were observed in the ability of these probiotics to bind to epithelial cells, indicating that the antagonist activity observed is specific to the pathogen tested and not a general defect of the product. Together, these data suggest that mechanisms of action of the yeast-based probiotics are dictated by variations of direct adhesion to pathogens. Further research is warranted to determine how these variations in binding potential influence the activity of these yeast-based probiotics in vivo.
Keywords:
probiotics, bacteria, yeast