Background: A simple and cost-effective method is needed for the detection of rifampicin resistance in Mycobacterium tuberculosis in resource-limited settings. We suggest a broth medium-based method using 2,3-diphenyl-5-thienyl-(2)-tetrazolium chloride (STC) for detection of rifampin resistance of tubercle bacilli within a reasonable time frame.

Methods: The type strain (M. tuberculosis H37Rv) and 45 cultured clinical strains of M. tuberculosis (35 rifampin-susceptible and 10 rifampin-resistant) were used. Phenotypes of rifampicin resistance were tested by the Korea Institute of Tuberculosis, and confirmed by GenoType MTBDRplus (Hain Lifescience, Germany). Susceptibility tests were performed using STC-containing OADC-enriched Middlebrook 7H9 broth (BD, USA).

Results: All tests were finished in 3 to 6 days. The same results were obtained with the standard and current methods for all 45 clinical isolates (100% sensitivity and specificity for resistance detection).

Conclusion: The current method using STC is a good alternative for detecting M. tuberculosis rifampin resistance in a cost-effective and timely fashion, which is particularly important in resource-limited settings. (Ann Clin Microbiol 2018;21:47-50)