TABLE 3.

Results of critical concentration testing of three methodsa

MethodLVX test concn (μg/ml)No. of isolates with susceptible results/No. susceptibleNo. of isolates with resistant results/No. resistant
BACTEC 46028/9b14/14
BACTEC MGIT 96029/914/14
AP123/24c13/14d
  • a Results of LVX critical concentration testing for the BACTEC 460, BACTEC MGIT 960 and AP methods. The critical test concentrations of LVX were chosen for each method based on results of testing clinical isolates of M. tuberculosis with known LVX susceptibilities. The selected critical test concentrations were then tested against a subset of LVX-susceptible M. tuberculosis isolates as well as isolates that were either clinically resistant to LVX or had known gyrA mutations associated with quinolone resistance.

  • b One isolate failed to grow in 12B medium.

  • c One 7H10 plate was unevaluable due to contamination.

  • d One isolate tested borderline resistant (1 to 10%). One isolate failed to grow on 7H10 medium.