The objective of this study was to perform a preliminary assessment of the potential antimicrobial effects in vitro of nutritional yeast culture (Diamond V XP™), containing Saccharomyces cerevisiae, media on which it was grown, and metabolites produced during fermentation. It was tested against Escherichia coli ATCC25922, Staphylococcus aureus ATCC25923, Candida tropicalis ATCC13803, and oral flora from human saliva. Serial dilutions of each microbe were mixed with either water or an aqueous extract of yeast culture, and plated on aerobic, coliform, or yeast/mold Petrifilm™, respectively. Colony counts and appearances showed that yeast culture induced strong inhibition of C. tropicalis growth, moderate inhibition of E. coli, and only minimal effect on growth of S. aureus or oral flora. Metabolic activity of E. coli was affected, as seen by reduced beta-glucuronidase activity and lack of gas formation indicative of lactose fermentation. The data suggest that yeast culture consumption may support beneficial composition of intestinal flora while promoting containment of some microbial species.