Performance of the Genotype MTBDR assay with isoniazid-resistant and -susceptible strains

Resistance or susceptibility by BACTEC 460TBNo. (%) of specimens
Genotype MTBDRkatG315 sequencinginhA sequencing
Mutation +Mutation −Unsuccessful amplificationMutation +Mutation −Mutation +Mutation −
High-level INH resistant (0.4 μg/ml) (n = 57)a48 (84.2)c8 (14)d1 (1.8)e49 (86)8 (14)2 (3.5)55 (96.5)
Low-level INH resistant (0.1 μg/ml) (n = 35)b2 (5.7)30 (85.7)3 (8.6)f2 (5.7)33 (94.3)18 (51.4)17 (48.6)
INH susceptible (n = 51)047 (92.2)4 (7.8)f051 (100)051 (100)
  • a A total of 42% of these strains were multidrug resistant.

  • b A total of 5.7% of these strains were multidrug resistant.

  • c One strain showed a wild-type and mutation probe-positive hybridization pattern together.

  • d In one of these strains, DNA sequencing identified a rare S315I mutation.

  • e Amplification was unsuccessful for three genes (M. tuberculosis complex-specific 23S rRNA, katG, and rpoB).

  • f Amplification was unsuccessful for two genes (M. tuberculosis complex-specific 23S rRNA and rpoB).