Results of Multiple Diagnostic Tests forMycobacterium aviumsubsp.paratuberculosisin Patients with Inflammatory Bowel Disease and in Controls
Authors: Collins Michael T. , Lisby Gorm , Moser Claus , Chicks Debra , Christensen Steen , Reichelderfer Mark , Høiby Niels , Harms Bruce A. , Thomsen Ole Ø. , Skibsted Ulrik , Binder Vibeke 
Published: December 2019

Mycobacterium aviumsubsp.paratuberculosishas been incriminated as a cause of Crohn's disease (CD); however, studies to date have been relatively small and generally only used a single diagnostic assay. The objective of the study was to reexamine the association ofM. aviumsubsp.paratuberculosisand CD using multiple diagnostic tests. Five methods were used to detectM. aviumsubsp.paratuberculosisinfections in 439 inflammatory bowel disease (IBD) patients and 324 control subjects in the United States and Denmark. Most assays were adaptations of diagnostic tests for this infection performed routinely on animals. PCR for IS900, a genetic element unique toM. aviumsubsp.paratuberculosis, was positive significantly more often on resected bowel and lymph node tissues from CD patients (19.0%) and ulcerative colitis (UC) patients (26.2%) than from controls (6.3%) (P< 0.05). Positive IS900PCR results occurred more often in U.S. than in Danish IBD patients, 32.0 versus 13.3% (P= 0.025). The majority of Danish patients were bacillus Calmette-Guérin (Mycobacterium bovisBCG) vaccinated (CD, 77.5%; UC, 86.6%; controls, 83.0%) whereas none of the U.S. patients with IBD and only 2% of U.S. controls were vaccinated. Among Danish IBD patients, positive PCR findings were four times more common among subjects who were not BCG vaccinated (33.3%) than among BCG vaccinates (8.8%,P= 0.02). Culture of the same tissues tested by PCR using modified BACTEC 12B medium failed to growM. aviumsubsp.paratuberculosisfrom patients or controls. U.S. CD patients had the highest serological evidence (enzyme-linked immunosorbent assay [ELISA] for serum antibodies) ofM. aviumsubsp.paratuberculosisinfection (20.7% of patients positive) which was higher than for all UC patients studied (6.1%) or healthy controls (3.8%,P< 0.005). Among Danish patients alone, however, no significant differences in rates of ELISA-positive results among CD, UC, or control patients were found. For 181 study subjects, both IS900PCR and ELISA were performed. Although 11 were ELISA positive and 36 were PCR positive, in no instance was a patient positive by both tests, suggesting that these states are mutually exclusive. Evaluation of cytokine-mediated immune responses of IBD patients was complicated by the influence of immunosuppressive therapy given most IBD patients. Gamma interferon (IFN-γ) release by peripheral blood leukocytes afterM. aviumpurified protein derivative PPD antigen stimulation showed significantly lower responses in CD patients than in UC patients or controls in both U.S. (by ex vivo assay) and Danish (by in vitro assay) populations (P< 0.05). Interleukin-5 responses were not different among CD, UC, or control groups. Collectively, the PCR, ELISA, and IFN-γ tests forM. aviumsubsp.paratuberculosistogether with the unexpected observation that BCG vaccination influencedM. aviumsubsp.paratuberculosisdetection, lead us to conclude thatM. aviumsubsp.paratuberculosis, or some similarly fastidious mycobacterial species, infects at least a subset of IBD patients. Whether the infection is primary (causal) or secondary, it may contribute to the etiopathogenesis of IBD.