Unraveling mechanisms of action of probiotics.

Probiotics are defined as living organisms that, when administered in sufficient numbers, are of benefit to the host. Current evidence indicates that varying probiotic strains mediate their effects by a variety of different effects that are dependent on the dosage employed as well as the route and frequency of delivery. Some probiotics act in the lumen of the gut by elaborating antibacterial molecules such as bacteriocins; others enhance the mucosal barrier by increasing the production of innate immune molecules, including goblet cell-derived mucins and trefoil factors and defensins produced by intestinal Paneth cells; and other probiotics mediate their beneficial effects by promoting adaptive immune responses (secretory immune globulin A, regulatory T cells, interleukin-10). Some probiotics have the capacity to activate receptors in the enteric nervous system, which could be used to promote pain relief in the setting of visceral hyperalgesia. Future development of the effective use of probiotics in treating various gastroenterological disorders in human participants should take advantage of this new knowledge. The creation of novel formulations of probiotics could be directed to effectively target certain mechanisms of actions that are altered in specific disease states.