Molecular and phenotypic characterization of multidrug-resistant Mycobacterium tuberculosis isolates resistant to kanamycin, amikacin, and capreomycin in China.

Although second-line anti-tuberculosis (TB) injectable drugs have been widely used to improve treatment outcomes of multidrug-resistant TB (MDR-TB), little is known about the prevalence and mechanism of second-line injectable drug resistance among MDR Mycobacterium tuberculosis isolates in China. Here, we found that 12.7 % (20/158) of isolates showed resistance to at least one second-line injectable drug among 158 MDR isolates. At the same time, there were 16 (10.1 %) strains resistant to kanamycin (KAN), 9 (5.7 %) to amikacin (AMK), and 12 (7.6 %) to capreomycin (CAP). In addition, our data revealed no significant difference in the drug resistance patterns for Beijing versus non-Beijing genotype strains (p > 0.05). The most frequently observed mutation was A-to-G substitution at position 1401 of the rrs gene, conferring high-level resistance to KAN and AMK, but had varying minimum inhibitory concentrations (MICs) for CAP. The mutations in the eis promoter and tlyA gene were responsible for low-level resistance to CAP. 83.3 % of A1401G substitutions in the rrs gene was observed in Beijing genotype strains, while the difference was not significant (p = 0.157). Our data demonstrated that the hot-spot regions localized in the rrs gene serve as excellent markers for AMK, but is not a sensitive marker for KAN and CAP. In addition, the cross-resistance patterns and MICs differed among different genetic mutation types, which challenge the practice in China of generalizing resistance to AMK and CAP based on the resistance to KAN alone. Our findings suggested that the individualized drug susceptibility to three major second-line injectable drugs is essential in order to generate more effective treatment regimens for MDR patients.