[Probiotics: from Metchnikoff to the current preventive and therapeutic possibilities]

About a century ago, Metchnikoff first hypothesised that some intestinal bacteria "produce compounds useful against a premature ageing". Since then, studies progressed over last century, leading to a remarkable improvement of the knowledge about the role of intestinal micro-organisms. Nowadays a number of different micro-organisms satisfying certain requisites are named probiotics and are produced on a large scale. At present, a rational use of probiotics with preventive and therapeutic purposes has been proposed not only for some gastrointestinal pathologies, such as the infective diarrhea (as recommended by the Italian Society of Pediatric, the Italian Society of Gastroenterology and Hepatology, the Italian Society of Pediatric Infectious Disease, and by International Societies), but also for other pathologic conditions, such as the atopic dermatitis and related affections (as suggested by the American Academy of Dermatology Association guide lines). Moreover, the use of probiotics is going to be extended to other pathologies, such as the inflammatory intestinal and respiratory diseases, and even to the prevention of tooth decay, although the actual preventive and therapeutic effects of probiotics onto these pathologies have to be carefully investigated. It is unknown if the genius Leonardo Da Vinci (1452-1519), stating that "man's life is built up by food" imagined how nutrients can influence human health, besides being essential for life, as it is today increasingly evident. Avoiding an excessive optimism and the thought that an efficacious panacea for all troubles has been found, there are sound reasons to believe that probiotics, and prebiotics as well, can influence human health, through the prevention and therapy of many diseases, although further studies are still requested to fully clarify the mechanisms of action of these micro-organisms on each pathology.