Probiotics in human medicine.

Probotics have been with us for as long as people have eaten fermented milks, but their association with health benefits dates only from the turn of the century when Metchnikoff drew attention to the adverse effects of the gut microflora on the host and suggested that ingestion of fermented milks ameliorated this so called autointoxication. Later work, based on the assumption that colonisation of the gut was essential for the maximum effect, used intestinal strains ofLacto-bacillus acidophilus for treatment ofconstipation. 1 The use of the term 'probiotic' to describe food supplements specifically designed to improve health, however, dates from 1974 when Parker used it to describe growth promoting animal feed supplements. He defined the term as 'organisms and substances which contribute to intestinal microbial balance'. I have recently2 revised this definition to read, 'A live microbial feed supplement which beneficially affects the host animal by improving its microbial balance'. This definition stresses the importance of viability and avoids the use of the too broad term 'substances' which could even include antibiotics. This report uses the revised definition and considers the evidence for the effect of live preparations on the human host. It also presents some evidence from work with animals which is helpful in understanding the potential benefits of this sort of treatment. Protecting effect of the gut microflora The belief in the beneficial effects of the pro-biotic approach is based on the knowledge that the intestinal microflora provides protection against various diseases. The evidence for this is incontrovertible and comes from several sources. Firstly, it can be shown that germ free animals are more susceptible to disease than are their conventional counterparts who carry a complete gut flora. This difference has been shown for infections caused by Salmonella enteritidis3 and Clostridium botulinum.4 For obvious reasons this sort of comparison cannot be made in human subjects, but it is reasonable to assume that at least some of these results would apply also to man. Another source of evidence that supports the protective effect ofthe gut flora is the finding that antibiotic treated animals, including humans, can become more susceptible to disease. In humans the disease pseudomembranous colitis, caused by Clostridium difficile, is almost always a consequence of antibiotic treatment.5 In rodents antibiotics have been shown to predispose to infections with Salmonella typhimurium6 Shigella flexneri, Vibrio cholerae,7 and C botulinum.8 The third source of supporting evidence comes from experiments in which …