Drug susceptibility testing of Mycobacterium tuberculosis against second-line drugs using the Bactec MGIT 960 System
C Rodrigues1, J Jani, S Shenai
1Department of Microbiology, P D Hinduja National Hospital and Medical Research Centre Tertiary Care Hospital, Mumbai, India. dr_crodrigues@hindujahospital.com
Objective:
To establish the critical test concentrations for seven second-line anti-tuberculosis drugs in the Bactec Mycobacterial Growth Indicator Tube (MGIT) 960 TB system and to evaluate its efficacy compared to the Bactec 460 TB system.
Design:
This study was carried out in three phases. In Phase I, pan-susceptible strains were tested to establish the minimum inhibitory concentration; in Phase II, mostly resistant strains were tested to determine a critical test concentration; and in Phase III, actual clinical isolates were tested to validate the optimal critical concentrations established in Phases I and II.
Results:
The critical concentrations established for seven second-line drugs with the Bactec MGIT 960 system are amikacin 1.0 microg/ml, capreomycin 2.5 microg/ml, kanamycin 2.5 microg/ml, ofloxacin 2.0 microg/ml, moxifloxacin 1.0 microg/ml, ethionamide 5.0 microg/ml and para-amino salicylic acid 4.0 microg/ml.
Conclusion:
The Bactec MGIT 960 System is an accurate and reliable method for rapid drug susceptibility testing (DST) of Mycobacterium tuberculosis against second-line drugs. In the present study, few of the strains were resistant to fluoroquinolones and further DST for this group is required.
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