Mycobacteria in Crohn's disease: DNA probes identify the wood pigeon strain of Mycobacterium avium and Mycobacterium paratuberculosis from human tissue

Mycobacterium paratuberculosis is known to cause Johne's disease, a granulomatous ileitis in ruminants, and may be involved in some cases of Crohn's disease. Like M. paratuberculosis, the wood pigeon strain of Mycobacterium avium may also show mycobactin dependence on primary isolation that is attenuated on further subculturing. A wood pigeon strain, M. avium restriction fragment length polymorphism (RFLP) type A/I, is also capable of causing granulomatous ileitis in experimental animal models but is not known to cause disease in humans. M. avium RFLP type A is associated with disease in immunocompromised hosts. Three DNA probes, pMB22 and the two subclones pMB22/S4 and pMB/S12, were found to be capable of distinguishing among M. paratuberculosis, M. avium type A, and M. avium type A/I (wood pigeon strain) on the basis of RFLPs. These DNA probes were used to identify two mycobacterial isolates (M. paratuberculosis and M. avium type A/I, wood pigeon strain) derived from the intestinal tissues of two patients with Crohn's disease. In addition, the wood pigeon strain of M. avium was identified from a patient with ulcerative colitis, and M. avium RFLP type A was identified from a patient with colonic carcinoma. This is the first time that M. avium A/I (wood pigeon strain) is known to have been isolated from human tissue. There are too few isolates to speculate about the etiological significance of mycobacteria and inflammatory bowel disease, but it is reasonable to conjecture that M. paratuberculosis may be responsible for some cases of Crohn's disease and that the wood pigeon strain of M. avium may also be an inflammatory bowel disease pathogen in humans.