Participation of iron on the growth inhibition of pathogenic strains of mycobacterium avium and M. paratuberculosis in serum.

Serum, which is low in freely-available iron, was bacteriostatic for M. avium and M. paratuberculosis irrespective of the ability of these organisms to produce the iron-chelators mycobactin and exochelin for iron acquisition. Bacteriostasis was overcome when the serum was supplemented with exochelin or mycobactin, but only if the mycobacteria had previously adapted to growth in a low iron environment. The results imply that for studies on mycobacterial pathogenicity the test cultures should be grown under low iron conditions before being used. The role of the exochelins, mycobactin and iron in the development of in vivo growth is discussed.