Bacterial milieu and mucosal bacteria in ulcerative colitis.

The aetiology of ulcerative colitis (UC) is unknown, but there is evidence that bacteria are needed for initiation and maintenance of the disease. A number of organisms have been associated with UC, but evidence for a specific transmissible agent is weak. Despite this, there is a good case for mucosal bacterial involvement, either through pathogens colonizing the epithelial surface, by non-pathogenic commensal species occupying adhesion sites on the mucosa and preventing invasion by harmful bacteria, or by inappropriate host immune responses to members of the normal microflora. Since mucosal bacteria exist in close juxtaposition to host tissues, it might be expected that they interact to a greater extent with the immune and neuroendocrine systems than their luminal counterparts. For this reason, comparative bacteriological analyses were done on rectal biopsies from patients with active colitis, and individuals who had no inflammatory bowel disease. Complex bacterial communities colonized the rectal mucosa in all subjects and great interindividual variabilities in mucosal bacterial populations were observed in both groups. These organisms often occurred in microcolonies, which may have implications for UC, since it would result in higher localized concentrations of bacterial antigens, or toxins, than would be the case if the organisms were diffusely spread across the mucosa.