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

Resistance or susceptibility by BACTEC 460TBNo. (%) of specimens
Genotype MTBDRrpoB sequencing
Mutation +Mutation −Unsuccessful amplificationMutation +Mutation −
Rifampin resistant (n = 26)a25 (96.2)c01 (3.8)e26 (100)0
Rifampin susceptible (n = 117)b3 (2.6)d102 (87.2)12 (10.2)f3 (2.6)114 (97.4)
  • a All strains were multidrug resistant.

  • b Fifty-one (43.6%) strains were pansusceptible, 33 (28.2%) strains were resistant to a high level (0.4 μg/ml) of isoniazid, and 33 (28.2%) strains were resistant to a low level (0.1 μg/ml) of isoniazid.

  • c Three strains showed a wild-type and mutation probe-positive hybridization pattern together.

  • d These strains showed susceptibility to RIF at concentrations of 2.0 μg/ml (reportable concentration) and resistance at concentrations of 0.5 μg/ml by the BACTEC 460TB system.

  • e Amplification was unsuccessful for one gene (rpoB).

  • f Amplification was unsuccessful for three genes (M. tuberculosis complex-specific 23S rRNA, katG, and rpoB) in one strain, for two genes (M. tuberculosis complex-specific 23S rRNA and rpoB) in seven strains, and for one gene (rpoB) in four strains.