Colony morphotypes on Congo red agar segregate along species and drug susceptibility lines in the Mycobacterium avium-intracellulare complex.

Isolates of the Mycobacterium avium-intracellulare complex (MAC) have long been known to segregate into transparent opaque and rough colony morphotypes that differ from each other in clinically important parameters including drug susceptibility and virulence. Here the authors report additional morphotypic variation that occurs on two levels: interspecific (between M. avium and M.