S. Mukherjee et al., The white morphotype of Mycobacterium avium-intracellulare is common in infected humans and virulent in infection models, J INFEC DIS, 184(11), 2001, pp. 1480-1484
Isolates of Mycobacterium avium-intracellulare (MAI) form multiple colony t
ypes named red-opaque, white-opaque, red-transparent (RT), and white-transp
arent (WT). The newly discovered WT morphotype is multidrug resistant relat
ive to other variants in vitro. To determine whether the WT morphotype occu
rs in humans, 32 MAI-positive clinical samples from 2 sites were plated dir
ectly onto indicator agar without prior passage in vitro. WT was the predom
inant morphotype in 26 (81%) of these samples and was absent in only 2 samp
les. WT variants grew better than isogenic RT variants in mouse and human m
acrophage models of infection, and RT clones that passed through such syste
ms underwent rapid shifts to the WT morphotype. The RT morphotype was heter
ogeneous with regard to infectivity. In summary, the white morphotype was c
ommon in humans and was favored in disease models. It may play an important
role in the establishment and persistence of MAI infection.