Evaluation of BACTEC 460 TB system for rapid in vitro screening of drugs against latent state Mycobacterium tuberculosis H37Rv under hypoxia conditions

Mycobacterium tuberculosis exhibits latent state due to its ability to survive for extended periods under oxygen depletion conditions. The conventional plating method employed for in vitro screening of antitubercular agents against latent state M. tuberculosis is laborious and time consuming exercise. Towards this end, BACTEC 460 TB system of antitubercular screening was evaluated for testing efficacy of antimicrobial agents in hypoxia induced model of latent tuberculosis, in vitro. In this study, drugs like isoniazid, metronidazole and rifampin were tested at concentrations— 2, 10 and 50 μg/ml for their antilatency activity by using BACTEC and conventional methods. Results obtained from both the methods were comparable (P > 0.05) and a good correlation was observed between colony forming units and growth index values. Further, time to determine mycobacterial growth was significantly reduced (P ≤ 0.001) in BACTEC method (4–7 days) as compared to plating method (26–30 days). BACTEC method was found to be faster, cost effective and more sensitive as compared to plating method. Being rapid, reliable and reproducible, this method can be a promising alternative to conventional plating method for screening of potential antitubercular agents in in vitro models of latent tuberculosis.