Molecular Mechanisms of Intrinsic Streptomycin Resistance in Mycobacterium abscessus.

Streptomycin, the first drug used for the treatment of tuberculosis, shows limited activity against the highly resistant pathogen We recently identified two aminoglycoside-acetylating genes [ and ] which, however, do not affect susceptibility to streptomycin. This suggests the existence of a discrete mechanism of streptomycin resistance. BLASTP analysis identified MAB_2385 as a close homologue of the 3″--phosphotransferase [APH(3″)] from the opportunistic pathogen as a putative streptomycin resistance determinant. Heterologous expression of in increased the streptomycin MIC, while the gene deletion mutant ΔMAB_2385 showed increased streptomycin susceptibility. The MICs of other aminoglycosides were not altered in ΔMAB_2385. This demonstrates that encodes a specific and prime innate streptomycin resistance determinant in We further explored the feasibility of applying -based streptomycin counterselection to generate gene deletion mutants in Spontaneous streptomycin-resistant mutants of ΔMAB_2385 were selected, and we demonstrated that the wild-type is dominant over the mutated in merodiploid strains. In a proof of concept study, we exploited this phenotype for construction of a targeted deletion mutant, thereby establishing an -based counterselection method in .