Probiotic microbes: do they need to be alive to be beneficial?

An essential symbiotic relationship exists between intestinal cells and commensal bacteria within the human gastrointestinal tract. Alteration or absence of this interaction may play a role in the development of human disease. Use of probiotic organisms has yielded improvement of certain medical conditions, such as inflammatory and infectious gastrointestinal disease, although the mechanisms of benefit remain poorly defined. The administration of live organisms is not without risk, both potential and realized, particularly in certain populations. Therefore, it is of considerable interest to determine if the health benefits of probiotics can be attained without the risks associated with administration of a live organism. Reviewed here is the evidence that heat-killed, ultraviolet-inactivated, and even components of these agents may be just as effective and considerably safer for the host.