Determination of the activity of standard anti-tuberculosis drugs against intramacrophage Mycobacterium tuberculosis, in vitro: MGIT 960 as a viable alternative for BACTEC 460.

BACTEC 460 has now been phased out, so the search for an alternative is imperative. We have determined the activity of standard anti-tuberculosis drugs against intramacrophage Mycobacterium tuberculosis, in vitro, by using BACTEC 460 and MGIT 960 methods. The minimum inhibitory concentrations of isoniazid, rifampicin, ethambutol and streptomycin against intracellular M. tuberculosis H37Rv were found to be 0.2, 0.8, 8.0, and 5.0 μg/mL, respectively, by both methods. These results show a significant (p<0.001) concordance between minimum inhibitory concentrations obtained by these two different methods. MGIT 960 system uses a robust florescence quenching-based oxygen sensor, requires no radioisotope, is safe, and relatively easy to operate. Apparently, this is the first report wherein MGIT 960 has been validated for anti-tubercular susceptibility testing against intracellular M. tuberculosis H37Rv. Our preliminary data thus clearly demonstrate that the MGIT 960 method can be considered as a promising alternative to BACTEC 460 method.