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The possible involvement of Mycobacterium avium ssp. paratuberculosis in the aetiology of Crohn's disease: a case control study in the NetherlandsHerrewegh AAPM; Overduin P; Roholl PJM; Gielis FK; Robinson JE; Mahmmod N; Lieverse RJ; Robijn RJ; Zanden AGM van der; Soolingen D van; et al. (Rijksinstituut voor Volksgezondheid en Milieu RIVM, 2005-11-25)A case control study was performed to investigate the possible role of Mycobacterium avium ssp. paratuberculosis (Map) in the aetiology of Crohn's disease (CD). Biopsy samples were collected from the ileum and colon of CD patients, Ulcerative Colitis (UC) patients and control persons. The biopsy samples were either cultured in MGIT and BACTEC medium, formaline-fixed, or immediately snap-frozen in liquid N2. The presence of Map bacteria in the cultures was determined using a nested PCR assay targeted to the conserved IS900 DNA-sequence of Map. 27% of CD patients, 6% of UC patients, and 28% of control persons were positive for MGIT-PCR. The BACTEC cultures resulted in a slightly smaller percentage of PCR positive patients, 22% for CD patients, 7% for UC patients and 25% for control persons. The presence of Map was further studied applying the IS900-PCR directly on DNA from frozen biopsy samples. 7% of CD patients, 8% of UC patients and 5% of control persons were PCR positive for Map. The presence of Map was also investigated in formalin-fixed biopsies samples using a hyperimmune antiserum to the M. avium-complex. With immunoperoxidase (IP) staining, M. avium-complex antigens were observed in biopsy samples from 20% of CD patients, 13% of UC patients and 29% of control persons. Surprisingly, these data show even a 50% higher presence of Map-antigens in control persons (29%) compared to CD patients (20%). Our data clearly show that Map is present both in IBD patients (CD and UC) and in control persons. The results of culturing and IP staining show a good correlation; with both techniques, an average of 23% of CD patients and 27% of control persons is positive for Map. Remarkably, the results of culturing and IP staining show an even higher prevalence of Map in control persons compared to CD patients. Moreover, only in a few instances patients were positive in two different tests (PCR, IP, MGIT and BACTEC), and even with both culturing assays almost no overlap in positive results is observed. This result indicates that the number of Map cells in human tissue is very low, and that the prevalence of Map in the population of IBD patients and of control persons is difficult to estimate. Unexpectedly, we obtained evidence that members of the Chlamydiales family are present in high amounts in most of the CD and UC patients, whereas they were of low incidence in control persons.In conclusion, our data do not support the hypothesis that Map is directly involved in Crohn's disease, but does not exclude that Map infection may play a role in the aetiology of Crohn's Disease for a susceptible subset of the population.