Probiotics have been well defined and long used in human and animal health and nutrition. Many of the probiotic strains used today have been isolated from the human gut flora, and it is therefore more a reintroduction of organisms rather than a novel concept. The beneficial effects of probiotics and, especially, the clinical use of probiotics in the management of specific diarrhoeal diseases, including Rotavirus diarrhoea, Traveller’s diarrhoea and others are well accepted[1
]. These effects are mainly based on colonisation resistance or the influence of probiotics on microflora balance. When discussing probiotics, it must be remembered that the intestinal microflora, resident in the large intestine, will always outnumber the probiotics that can be administered. Furthermore, probiotic processes will always be confounded by the diversity of the human microbiota and its variability in the face of varied human diets and genetic backgrounds[2
Within the human gut, we have to separate processes occurring in the distal small intestine from those happening in the colon. The small intestine harbours relatively low numbers of resident intestinal bacteria, but at the same time contains the major part of the gut associated lymphoid tissue (GALT), which samples intestinal microbes[3
]. Hence modulation of systemic immune and allergic phenomena might be primarily mediated by the GALT of the small bowel. Supplementing qualitatively and quantitatively optimised microbes to this part of the gut might stimulate Treg cell development and consequent immunomodulation[1
]. Within the large intestine, bacterial intervention might cause modulation of the microbial fermentation activity and direct action on the colonic epithelium to alter (suppress) innate immunity. These processes might explain the impact of probiotics on inflammatory and functional bowel disorders.
The research field of probiotics is very heavily reviewed, using different clinical and microbiological angles to elucidate the topic. The aim of this review is to summarise the most recent trends in probiotic research, focusing on the clinical use of probiotics and their effects on the healthy and diseased gut and liver.
The direct and indirect actions of probiotics on intestinal cells and their consequences on liver (summarised in Figure ) will be discussed in this review.
Figure 1 Potential mechanisms of action by which probiotics can promote GI health and the consequences for the liver. Probiotics and surface-layer proteins competitively exclude microbial pathogens from mucosal surfaces. Tight junction proteins, such as zona occludins-1 (more ...)