Introduction
The Mycobacterium avium complex (MAC) comprises several species of slow-growing mycobacteria that are prevalent in environmental, veterinary and clinical settings. The MAC includes professional pathogens of birds and livestock, opportunistic pathogens of humans, as well as organisms commonly found in soil and water. Historically, classification of MAC organisms was based on phenotypic features, including growth characteristics, source of isolation and virulence in experimental animals. Molecular taxonomy approaches have challenged traditional designations and transformed our view of the MAC. Although Mycobacterium paratuberculosis was once considered a separate species, current taxonomy classifies it as M. avium subsp. paratuberculosis (MAP), a pathogenic clone of the MAC.
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