Living drugs for gastrointestinal diseases: the case for probiotics

Nonpathogenic micro-organisms may contain or produce molecules of potential therapeutic interest. This led to the concept of using ingested living micro-organisms to produce and transport these molecules to targets in the proximal or distal intestine. Several characteristics of this pharmacological approach are very original: potential for in vivo production of active molecules, for targeting immune cells, for presenting immunogenic molecules in a microbial context, for duodenal delivery using bile sensitivity. Probiotics have been studied for some decades and more recently worm eggs have also received some interest. This paper summarizes facts (especially results of randomized controlled trials and pharmacokinetic studies), and ideas about the use of probiotics to treat or prevent gastrointestinal diseases. The safety of this approach (exceptional cases of infections have been observed), and the potential for using new agents or genetically modified micro-organisms (ongoing trials in humans with Crohn's disease) are also discussed.