The role of eis mutations in the development of kanamycin resistance in Mycobacterium tuberculosis isolates from the Moscow region.

OBJECTIVES: Kanamycin is an important second-line drug used to treat multidrug-resistant (MDR) tuberculosis (TB). Molecular analysis of the rrs gene seems to be not enough to identify every case of kanamycin resistance. In the present study we evaluated the incidence of eis mutations in kanamycin-resistant Mycobacterium tuberculosis isolates.
METHODS: We analysed 70 MDR M. tuberculosis clinical isolates. All isolates were screened for rrs and eis mutations using single-strand conformation polymorphism and sequencing. Phenotypic drug susceptibility testing was performed using Bactec MGIT 960 and the absolute concentration method on Lowenstein-Jensen medium.
RESULTS: eis mutations were found in 10 isolates. The most prevalent mutations were the A1401G substitution in the rrs gene and the C14T substitution in the eis promoter region.
CONCLUSIONS: Our study shows that the eis promoter region is a useful molecular marker of kanamycin resistance in the Moscow region. Complex analysis of rrs and eis mutations will significantly reduce the time to diagnose kanamycin resistance in TB patients, compared with phenotypic drug resistance testing.