A nutritional supplement containing the probiotic bacterium Lactobacillus plantarum 299 (Lp 299) with potential antimicrobial, immune-boosting, and anti-inflammatory activities. Upon oral ingestion, Lp 299 adheres to the intestinal mucosa, modulates the composition of the normal microflora, helps maintain adequate colonization of the gastrointestinal (GI) tract and improves digestion and metabolism. Upon colonization of the GI tract, the probiotic may form a protective barrier, thereby preventing attachment of pathogens, protecting against infections and boosting the immune system. In addition, Lp 299 stimulates the secretion of protective mucin and produces lactic acid and hydrogen peroxide as well as other substances, thereby creating an acidic environment which prevents growth of pathogens.