Paradoxical effect of Tween 80 between the susceptibility to rifampicin and streptomycin and the susceptibility to ethambutol and sulfadimethoxine in the Mycobacterium avium-Mycobacterium intracellulare complex.

The susceptibility to rifampicin and streptomycin of the Mycobacterium avium-Mycobacterium intracellulare complex was augmented by the addition of Tween 80 into 7H10 agar medium with OADC, whereas the susceptibility to ethambutol and sulfadimethoxine was either not changed or reduced by the addition of Tween 80. In 7H10 agar medium without OADC, however, susceptibilities to both rifampicin and sulfadimethoxine were reduced by the addition of Tween 80 to the medium. A number of hypotheses are made to explain these phenomena.