Mycobacterium avium subspecies paratuberculosis and Crohn's disease granulomas

OBJECTIVE: Chronic infection with Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) has been proposed as a cause of Crohn's disease. Although numerous investigators have examined the link between M. paratuberculosis and Crohn's disease, the evidence remains controversial. The aim of this study was to examine intestinal granuloma from Crohn's patients for M. paratuberculosis using a semi-nested M. paratuberculosis-specific IS900 polymerase chain reaction (PCR). MATERIAL AND METHODS: Paraffin-embedded ileal or colonic tissues of patients with Crohn's disease were analyzed. Microdissection of this tissue into "granulomas" and "not granulomas" was performed. On the basis of sequences reported in GenBank alignments, we designed primer sets specific for M. paratuberculosis. The presence of the M. paratuberculosis was examined by semi-nested IS900-specific PCR with human beta-actin gene as a control for DNA quality. RESULTS: Biopsies from 20 Crohn's patients were examined. Human beta-actin gene was amplified in all samples. M. paratuberculosis DNA was detected in the microdissected granuloma in 1 (5%) patient with Crohn's disease and in none of the "not granuloma" tissues. CONCLUSIONS: M. paratuberculosis DNA can rarely be detected within Crohn's granuloma. These results do not support M. paratuberculosis as the primary etiology of Crohn's disease.