FIG 6.

MAB_4532c is induced exclusively in M. abscessus as part of the whiB7 regulon and confers amikacin (Amk) resistance. (A) Heterologous expression of MAB_4532c (eis2) from a constitutive promoter integrated at the L5 attB site increases amikacin and kanamycin resistance of M. smegmatis from 0.4 μg/ml to 8 μg/ml. Similar overexpression of MSMEG_4540 (eis2) is insufficient to enhance amikacin/kanamycin resistance in M. smegmatis. (B to E) Wild-type M. smegmatis and M. abscessus and the ΔMabwhiB7 mutant were grown to an A₆₀₀ of 0.7, exposed to sublethal concentrations of amikacin, as indicated, and the amount of whiB7, eis1, and eis2 transcripts were determined by qPCR and plotted as fold induction over an unexposed control. Data represent the mean ± SD, n = 3. Although whiB7 is induced in both bacteria, eis2 is induced only in M. abscessus in a whiB7-dependent manner and confers species-specific amikacin sensitivity.