Gut microbiota promotes healthy effects on the host and prevents diseases. Probiotic (probios, for life) are defined as “live microorganisms which when administered in adequate amounts confer a health benefit on the host.” At the beginning of 1900s Louis Pasteur identified the microorganisms responsible for the process of fermentation, whereas E. Metchnikoff associated the enhanced longevity of Bulgarian rural people to the regular consumption of fermented dairy products such as yogurt. He suggested that lactobacilli might counteract the putrefactive effects of gastrointestinal metabolism that contributed to illness and aging. Hippocrates declared, 2000 years earlier, that “death sits in the bowels.” Metchnikoff considered the lactobacilli as probiotics (“probios,” conducive to life of the host as opposed to antibiotics); probiotics could have a positive influence on health and prevent aging. During the neolitic period of the age of the stone, the domestication of animals occurred and man began to get fermented food. Probably serendipitous contaminations in favorable environments played a major role. Fecal microbiota transplantation dates to a fourth-century Chinese handbook for food poisoning or severe diarrhea. To date fecal transplant cures Clostridium difficile infections with more efficacy than vancomycin, and prevents recurrence.