The intestinal mucus layer from patients with inflammatory bowel disease harbors high numbers of bacteria compared with controls

Background & Aims: Whether the bacterial flora contributes to the pathogene sis of inflammatory bower disease (IBD) by increased penetration in mucus, increased adherence to epithelial cells, or invasion of the epithelium is u nknown. We therefore studied the spatial distribution of bacteria in the mu cosa of rectal biopsy specimens from patients with IBD and from controls. M ethods: Rectal biopsy specimens from 19 patients with IBD and from 14 contr ols were studied by using nonradioactive ribosomal RNA in situ hybridizatio n. Total mucosal surface length examined for each patient was measured, and the number of bacteria visualized was estimated semiquantitatively. Result s: No bacteria were observed in biopsy specimens from 10 controls (71%) and 6 IBD patients (32%) (P = 0.04; odds ratio, 5.42; 95% confidence interval, 1.23-23.9). IBD rectal specimens contained significantly more bacteria tha n control samples (P = 0.004). Bacteria were localized within the mucus lay er but did not adhere to the epithelial cells and were not present within t he lamina propria. There was no correlation between the numbers of bacteria present and either the degree of inflammation or the use of antiinflammato ry agents or sulfasalazine compounds. Conclusions: The intestinal mucus in IBD patients is less protective against the endogenous microflora than in c ontrols, resulting in increased association of luminal bacteria with the mu cus layer.