Mycobacterium avium paratuberculosis in Italy: commensal or emerging human pathogen?

Background: Specific bacterial infections or alterations of the gut microbiota likely trigger immuno-pathological phenomena associated with Crohn's disease and ulcerative colitis. Mycobacterium avium subspecies paratuberculosis is a candidate etiological agent of Crohn's disease. Definitive causal connection between Mycobacterium avium subspecies paratuberculosis infection and Crohn's disease has not been demonstrated.

Aims: To determine the circulation of Mycobacterium avium subspecies paratuberculosis in Crohn's disease patients and water supplies in an Italian region where this bacterium is endemic in cattle farms.

Methods: Mycobacterium avium subspecies paratuberculosis screening was performed on biopsies from human patients, and from water samples, using two different PCR procedures.

Results: In hospitals where multiple specimens were obtained from different sites in the intestine, the prevalence of Mycobacterium avium subspecies paratuberculosis infection was 82.1% and 40% respectively in Crohn's disease and ulcerative colitis patients; in another hospital, where single specimens were obtained from patients, the bacterium was not detected. Control subjects also harboured Mycobacterium avium subspecies paratuberculosis, but at a lower prevalence. Tap water samples collected in the study area contained Mycobacterium avium subspecies paratuberculosis DNA.

Discussion: The results of screenings for Mycobacterium avium subspecies paratuberculosis in humans are deeply influenced by both the number and location of the collected biopsies. There is a wide circulation of the organism in the study area, considering the prevalence in humans and its presence in drinking water.