Role of probiotics in the treatment of intestinal infections and inflammation

Probiotics in inflammatory bowel disease--therapeutic rationale and role

The intestinal flora has a conditioning effect on intestinal homeostasis, delivering regulatory signals to the epithelium, the mucosal immune system and to the neuromuscular activity of the gut. Beneficial metabolic activities of the enteric flora include nutrient production, metabolism of dietary carcinogens, conversion of prodrugs to active drugs. However, increasing evidence suggests that some components of the enteric flora are essential ingredients in the pathogenesis of inflammatory bowel disease (IBD); this has prompted interest in therapeutic manipulation of the flora with probiotics. Probiotics are biologic control agents-described as live microbial food supplements which confer a health benefit beyond inherent basic nutrition. Multiple potential beneficial effects have been attributed to the probiotic use of lactic acid bacteria, bifidobacteria and other non-pathogenic commensals. At present, much of the promise of probiotics remains outside the realm of evidence-based medicine and awaits the results of prospective trials, now underway. No reliable in vitro predictors of in vivo efficacy of putative probiotics have been identified. Rigorous comparisons of probiotic performance have not been performed and the suitability of a given probiotic for different individuals is largely unexplored. Notwithstanding, an improved understanding of the normal commensal flora and host-flora interactions has the potential to open up new therapeutic strategies for inflammatory disorders of the gut.

Short fractions of oligofructose are preferentially metabolized by Bifidobacterium animalis DN-173 010

The growth of Bifidobacterium animalis DN-173 010 on different energy sources was studied through small- and large-scale fermentations. Growth on both more common energy sources (glucose, fructose, galactose, lactose, and sucrose) and inulin-type fructans was examined. High-performance liquid chromatography analysis was used to investigate the kinetics. Gas chromatography was used to determine the fructan degradation during the fermentation process. B. animalis DN-173 010 was unable to grow on a medium containing glucose as the sole energy source. In general, monosaccharides were poor growth substrates for the B. animalis strain. The fermentations with the inulin-type fructans resulted in changes in both growth and metabolite production due to the preferential metabolism of certain fructans, especially the short-chain oligomers. Only after depletion of the shorter chains were the larger fractions also metabolized, although to a lesser extent. Acetic acid was the major metabolite produced during all fermentation experiments. At the beginning of the fermentation, high levels of lactic acid were produced, which were partially replaced by formic acid at later stages. This suggests a shift in sugar metabolism to gain additional ATP that is necessary for growth on oligofructose, which is metabolized more slowly.

Probiotics: a perspective on problems and pitfalls

Therapeutic manipulation of gut flora with probiotics promises to be a useful strategy for several disorders, including infectious, inflammatory and neoplastic conditions. However, there are large gaps in the knowledge of the normal flora and of the optimal use of probiotic products. At present, there is no reliable in vitro predictor of in vivo efficacy of putative probiotics. Indeed, probiotic performance should be defined in the context of the disease indication for which it is intended. This will require rigorous prospective clinical trials. In addition, guidelines for routine clinical use of probiotics are confounded by insufficient data on optimum strain selection, dose, delivery vehicle and monitoring. Before the promise can be fulfilled, problems and potential pitfalls with probiotic therapy need resolution.

The host-microbe interface within the gut

Colonization with bacteria is critical for the normal structural and functional development and optimal function of the mucosal immune system. Unrestrained mucosal immune activation in response to bacterial signals from the lumen is, however, a risk factor for inflammatory bowel disease. Therefore, mucosal immune responses to indigenous flora require precise control and an immunosensory capacity for distinguishing commensals from pathogens. The use of germ-free animal models with selective colonization strategies combined with modern molecular techniques promises to clarify the molecular signals responsible for host-flora interactions in health and disease. At least half of the resident flora cannot be cultured by conventional techniques but are identifiable by molecular methods. Collectively, the resident flora represent a virtual organ with a metabolic activity in excess of the liver and a microbiome in excess of the human genome. An improved understanding of this hidden organ holds secrets relevant to several infectious, inflammatory and neoplastic disease mechanisms.