Increased expression of Mycobacterium tuberculosis Rv3737 gene associated with low-level amikacin resistance

As an infectious disease, tuberculosis (TB) poses a serious threat to public health. Although amikacin (AMK) is an important antibiotic for the treatment of drug-resistant TB, its resistance mechanisms are not fully understood.

To investigate the role of Rv3737 gene on AMK drug susceptibility, a Mycobacterium tuberculosis (M.tb) Rv3737 knockout strain (H37Rv△Rv3737) and a Mycobacterium smegmatis (M.sm) Rv3737 overexpressing strain (Msm/pMV261-Rv3737) were used to detect their minimal inhibitory concentrations (MICs) in this study.

The AMK MICs of Rv3737 knockout and overexpressing strains were 4-fold lower and 2-fold higher than those of the wild-type and empty plasmid strains, respectively. The results of clinical isolates showed that no Rv3737 gene mutation was found to be associated with AMK susceptibility, while the rrs A1401G mutation remained the main mechanism of high level of AMK resistance (MIC>32 μg/ml). There was a positive correlation between Rv3737 mRNA expression level and AMK MIC. In the isolates with low-level AMK resistance (MIC = 4 μg/ml) without rrs A1401G mutation, the expression level of Rv3737 gene was significantly higher than those of susceptible isolates.

In this study, the Rv3737 gene was reported for the first time for its effect on AMK susceptibility in M.tb. Although the rrs A1401G mutation remains the main reason of high-level AMK resistance, high expression of the Rv3737 gene was associated with low-level AMK resistance in clinical isolates.