Comparative study of the intestinal mucous barrier in normal and inflamed colon

Alexander Swidsinski ^1*, Vera Loening-Baucke ¹, Franz Theissig ², Holger Engelhardt ², Stig Bengmark ³, Stefan Koch ², Herbert Lochs ¹ and Yvonne Doerffel ¹

¹ Humboldt University, Berlin, Germany
² Humaine Klinikum Bad Saarow/Fürstenwalde, Germany
³ UCL Institute of Hepatology University College, London Medical School, United Kingdom

^* To whom correspondence should be addressed. E-mail: alexander.swidsinski{at}charite.de.

Accepted 1 August 2006

Abstract

Background and Aims: To study the role of mucus in the spatial separation of intestinal bacteria from mucosa.

Patients and Methods: Mucus barrier characteristics were evaluated in histologic material obtained by biopsy from purged colon, colon prepared with enema and material of untreated appendices fixated with non-aqueous Carnoy solution. Bacteria were evaluated using fluorescent in situ hybridization with bacterial 16S RNA probes and related to the periodic acid/Schiff (PAS) alcian blue stain. Biopsies from normal controls (N=20), patients with self-limiting colitis (SLC/N=20), ulcerative colitis (UC/N=20) and 60 appendices randomly selected were investigated.

Results: The mucosal surface beneath the mucus layer was free of bacteria in 80% of the normal appendices and biopsies from normal controls. The thickness of the mucus layer and its spread decreased with increasing severity of the inflammation; the epithelial surface showed bacterial adherence, epithelial tissue defects and deep mucosal infiltration with bacteria and leukocytes. Bacteria and leukocytes were found within mucus in all biopsies from patients with UC, SLC and acute appendicitis. The concentration of bacteria within mucus was inversely correlated to the numbers of leukocytes.

Conclusions: The large bowel mucus layer effectively prevents contact between the highly concentrated luminal bacteria and the epithelial cells in all parts of the normal colon. Colonic inflammation is always accompanied by breaks in the mucus barrier. Although the inflammatory response gradually reduces the number of bacteria within mucus and feces, the inflammation itself is not capable to prevent bacterial migration, adherence to and invasion of the mucosa.

Keywords: FISH, IBD, colonic mucus, mucosal bacteria, mucus barrier

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