Different correlations of drug susceptibilities to colonial morphology in Mycobacterium avium complex strains

In Mycobacterium avium and Mycobacterium intracellulare complex strains isolated from patients who were not treated previously by any antituberculosis drugs or from fowls, the colonial morphology, smooth, domed, opaque (SmD) or smooth, flat, transparent (SmT) colonial forms, significantly correlated with susceptibilities to rifampicin, minocycline, streptomycin, kanamycin, enviomycin, ethambutol, and sulfadimethoxine, whereas it did not correlate with susceptibilities to isoniazid, cycloserine, and ethionamide. Strains with the SmT colonial morphology were more resistant to the former seven drugs than strains with the SmD colonial morphology. Since the susceptibilities to antituberculosis drugs with large molecules correlated with the colonial morphology, it has been suggested that a permeability barrier that allows passage of small molecules but prevents passage of large molecules exists in the strains with the SmT colonial morphology.