I found this on the probiotic lifespan discussion:
Probiotics, just like other forms of life, have a lifespan. Under favorable conditions, probiotics can live until the cells naturally undergo replacement or renewal. According to Gary Huffnagle, author of the “The Probiotic Revolution,” probiotics attached to immune cells in the digestive tract can live up to a week. Immune cells renew about every 6 or 7 days.
Probiotics need a favorable environment in order to live out their expected or hopeful lifespan. Certain foods and substances can either increase or decrease the lifespan of probiotics. Prebiotics are substances that promote colonization and reproduction of beneficial bacteria. Some prebiotics include kale, flax, barley, bananas, honey, garlic, lactic acid and Inulin. On the other hand, toxins and chemicals can cause premature probiotic death. Some of these chemicals include alcohol, food additives, stress, certain medications and sugar — including sugar substitutes. A healthy, balanced diet will prevent premature death