This bacterium is the cause of Johne’s disease. Molecular taxonomists prefer to name this organism Mycobacterium avium subspecies paratuberculosis (MAP) in recognition of its close genetic similarity to other Mycobacterium avium subspecies, collectively known as the Mycobacterium Avium Complex. Three characteristics distinguish MAP from other mycobacteria: 1) an in vitro (laboratory culture) growth requirement for mycobactin, an iron transport chemical produced all other mycobacteria, 2) very slow growth rate (this is the slowest growing of all culturable mycobacteria known to microbiologists), and 3) presence of a genetic element in the chromosome of the organism called IS900.
