Probiotics in human disease.

Western civilization is facing a progressive increase in immune-mediated, gut-related health problems, such as allergies and autoimmune and inflammatory diseases, and genetic factors are an unlikely explanation for these rapid increases in disease incidence. Two environmental factors that relate to the modern lifestyle in Western societies are hygiene and nutrition. There has been a decline in the incidence of microbial stimulation by infectious diseases as a result of improved hygiene, vaccination, and antimicrobial medication. In the past, methods of food preservation involved either the natural fermentation or drying of foods; thus, the human diet once contained several thousand times more bacteria than it does today. The development of probiotic, functional foods aims to "kill two birds with one stone," which is accomplished by providing a microbial stimulus to the host immune system by means of beneficial live microorganism cultures that are characteristic of the healthy, human gut microflora, ie, probiotics. Probiotic bacteria were shown to reinforce the different lines of gut defense, which are immune exclusion, immune elimination, and immune regulation. They were also shown to stimulate nonspecific host resistance to microbial pathogens, thereby aiding in pathogen eradication. Consequently, the best documented clinical application of probiotics is in the treatment of acute diarrhea. In humans, documented effects were reported for the alleviation of intestinal inflammation, normalization of gut mucosal dysfunction, and down-regulation of hypersensitivity reactions. These data show that probiotics promote endogenous host defense mechanisms. Thus, modification of gut microflora by probiotic therapy may offer a therapeutic potential in clinical conditions associated with gut-barrier dysfunction and inflammatory response.