Linskens RK, Huijsdens XW, Savelkoul PHM, Vandenbroucke-Grauls CMJE, Meuwissen SGM. The bacterial flora in inflammatory bowel disease: current insights in pathogenesis and the influence of antibiotics and probiotics. Scand J Gastroenterol 2001;36 Suppl 234:29-40.The pathogenesis of in ammatory bowel disease (IBD) remains unknown, although in recent years more data have become available. The contribution of genetic and environmental factors is evident, and the luminal bacterial ora plays a major role in the initiation and perpetuation of chronic IBD. Animal models of IBD have shown that colitis does not occur in a germ-free environment. In human IBD, in ammation is present in parts of the gut containing the highest bacterial concentrations. Moreover, the terminal ileum, caecum and rectum are areas of relative stasis, providing prolonged mucosal contact with luminal contents.Enhanced mucosal permeability may play a pivotal role in maintaining a chronic in ammatory state, due to a genetic predisposition or as a result of direct contact with bacteria or their products. A defective epithelial barrier may cause a loss of tolerance to the normal enteric ora. Furthermore, an increased mucosal absorption of viable bacteria and bacterial products is found in IBD. Serum and secreted antibodies are increased and mucosal T-lymphocytes that recognize luminal bacteria are present. However, there is evidence that the immune system reacts over aggressively towards the normal luminal ora rather than the ora being altered in IBD. Several approaches have been used in attempts to discover a speci c microbial agent in the cause of IBD. These include demonstration of the presence of organisms or speci c antigens in affected tissues, culture of microbes from the affected tissues, demonstration of serological responses to several agents, and localization and detection of individual pathogen-speci c nucleic acid sequences in affected tissue by in situ hybridization and polymerase chain reaction. So far, no speci c micro-organism has been directly associated with the pathogenesis of IBD. Analysis of the luminal enteric ora, however, has revealed differences in the composition of this ora compared to healthy controls. In Crohn disease, concentrations of Bacteroides, Eubacteria and Peptostreptococcus are increased, whereas Bi dobacteria numbers are signi cantly reduced. Furthermore, in ulcerative colitis, concentrations of facultative anaerobic bacteria are increased. The arrival of new molecular techniques qualifying and quantifying the complex intestinal ora has induced a revival of interest in this micro ora.Therapeutic approaches geared towards changing the environment at the mucosal border have been attempted by the use of elemental diets, total parenteral nutrition, surgical diversion of the faecal stream and antibiotics. Over the past few years, the use of probiotics in IBD and other intestinal disorders has gained attention. Strengthened by promising experimental data and commercial interests, research in this eld is rapidly expandin...