For decades, it has been believed that consumption of fermented dairy products is beneficial for health. In 1907, Eli Metchnikoff, the Nobel Prize winner and director of the Pasteur Institute, postulated in his book The Prolongation of Life that eating yogurt would extend the life span due to the health-improving influence of the lactic acid bacteria (LAB) involved in yogurt fermentation on the gut flora. Since that time, many studies have been conducted on gut-associated microorganisms, of which LAB are important members (1- 3). These studies have led to the growing recognition today that the microflora colonizing the gastrointestinal tract of man and animal indeed play an important and essential role for the health of the host.