Douglas Laboratories Multi-Probiotic 15 Billion contains over 15 billion beneficial organisms from lactobacillus and bifidobacterium genera with additional benefits of prebiotic fructooligosaccharides. Oral supplements of live, beneficial intestinal microorganisms for nutritional health and well-being are known as probiotics. Probiotic dietary lactobacilli colonize the intestinal tract. Bacteria are continually in competition for colonization space. The original bacterial colonies have an advantage over transient bacteria. Nevertheless, the composition of the intestinal microflora is dynamic and constantly changing. If harmful microorganisms proliferate, the equilibrium is disturbed, and it becomes difficult even for indigenous bacteria to maintain their necessary territory to colonize the intestine. Antibiotics tend to kill off both beneficial and harmful bacteria, and thus may also disturb the normal, healthy balance of intestinal microorganisms. Various intestinal conditions can compromise the immune system and lower the amounts of healthy intestinal microflora. When potent probiotic supplements, such as Multi-Probiotic 15 Billion, are supplied regularly, chances are greatly increased for establishing and maintaining a healthy population of beneficial intestinal microorganisms. Once established, a normal intestinal microflora rich in lactobacilli creates acidic conditions that are unfavorable for the settlement of pathogenic microorganisms.