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Imani Fooladi et al. combined the two aforementioned methods (Middlebrook 7H9 broth, L–J medium) and suggested the modified broth dilution method for the DST of M. tuberculosis against heat-labile anti-TB drugs. They only evaluated this method on M. tuberculosis strain H37Rv and a few other strains . Since the study size was small, it is necessary to evaluate this method in a larger population to come to a more accurate and acceptable conclusion. To our knowledge, a large-scale evaluation of this modified method has not been assayed. The present study utilized a considerable number of strains, which were tested to determine the validity of this modified method. The results showed that this modified method could ease susceptibility testing of M. tuberculosis against new lipophilic antitubercular agents in less-equipped laboratories, especially because it requires no high technology or high cost. However, there are some limitations, such as a 5–7 week waiting NVP-TNKS656 manufacturer for final results, a requirement for two different mediums and greater amounts of manipulation, which can be hazardous. This modified assay proved to be an ideal method for preclinical susceptibility testing and determination of the exact MBCs as well as percent of inhibition of new antitubercular agents, especially heat-labile or/and lipophilic compounds. Although, utilization of this modified method for the susceptibility testing of first-line anti-TB drugs (e.g. rifampicin, which experiences some inactivation in L–J medium) may inhibit partial inactivation of the drug by the culture medium; however, before this method can be performed for routine drug susceptibility, further investigations are needed.The complete agreement between the results obtained from the modified broth-based method and the proportional L–J medium in the susceptibility testing of 114 strains of M. tuberculosis against isoniazid suggests that big bang theory modified method is reliable and has validity, compared with the gold standard L–J method.Considering the failure of the standard method for the susceptibility testing of lipophilic antitubercular drugs, and the reliable results obtained using the modified broth-based method, we conclude that performance of the modified method can diminish the interference effect of an L–J medium on lipophilic antitubercular drugs. The modified broth-based method is sensitive, inexpensive, non radiometric, and offers the potential for screening without high technology instrumentation. Therefore, this modified method could be recommended for the susceptibility screening of M. tuberculosis against not only heat-labile drugs as mentioned by Imani et al.  but also lipophilic compounds candidate as antitubercular agents.Conflict of interestThere is no conflict of interest related to the material in the manuscript.AcknowledgmentThe authors owe their gratitude to Mashhad University of Medical Sciences Vice Chancellor of Health for permission to use their laboratory in this study. We thank Mahmoud Seifi, Vahid Abasi, and Hasan Afzali for their excellent technical assistance. This work was part of Ph.D thesis of Mehdi Zandhaghighi. Mashhad University of Medical Sciences has supported this work.