• Crohn's disease;
  • etiology;
  • inflammatory bowel disease;
  • Listeria;
  • ulcerative colitis

Abstract Background and Aims: Components of the intestinal microflora are believed to play an important role in the pathogenesis of inflammatory bowel disease (IBD) in genetically susceptible hosts acting either as a non-specific antigenic stimulus or as a specific pathogen. Listeria monocytogenes has been suggested as an organism with the potential to cause IBD. The objective of the present study was to investigate the prevalence of L. monocytogenes DNA in intestinal biopsies from patients with IBD and from non-IBD controls by using nested polymerase chain reaction (PCR).

Methods: The DNA was extracted from 274 colonoscopic biopsies, which were obtained from 23 patients with Crohn's disease (CD), 28 with ulcerative colitis (UC) and 39 non-IBD control patients. Nested PCR amplification was used to detect the presence of the L. monocytogenes listeriolysin O (hly) gene. The sequences of positive PCR products were determined and compared with databases.

Results: The sensitivity of our nested PCR was 10 fg L. monocytogenes DNA. Overall, L. monocytogenes DNA was detected in 13.0% patients with CD, 17.9% patients with UC and 25.6% non-IBD control patients or in 29 of 274 (10.6%) endoscopic biopsies. Among them, L. monocytogenes DNA was detected in four of 67 (6%) biopsies from patients with CD, five of 94 (5.3%) biopsies from patients with UC and 20 of 113 biopsies (17.7%) from non-IBD control patients. Sequence analysis of positive PCR products demonstrated more than 95% similarity to the hly gene sequence of L. monocytogenes, confirming the authenticity of our PCR products.

Conclusion: Listeria monocytogenes DNA was detected in the intestine of both patients with IBD and in non-IBD control patients, probably reflecting the widespread presence of this organism in the environment. The low yield of positive biopsies in our IBD patients (5–6%) and the fact that the detection rate of L. monocytogenes DNA was similar in endoscopic biopsies from IBD patients and non-IBD controls does not support a direct role for L. monocytogenes in the pathogenesis of IBD, at least in New Zealand patients.