Abstract
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)
Keywords
Drug susceptibility test Mycobacterium tuberculosis Rifampin resistance
Figures & Tables
Fig. 1. Eppendorf tubes showing rifampin resistance. (A, C) shows insoluble STC precipitates, and (B, D) shows pink colored solution after adding the solubilizing agent. (A) resistant, or dark precipitates in the bottoms of each tube; (C) susceptible, or no precipitate in left 3 tubes; (B) resistant, or pink colored media; (D) susceptible, or no color change in left 3 tubes.
Figures & Tables
Table 1. Results of STC-based rifampin resistance detection method
| Tubes of rifampin concentration (mg/mL) | No. of tubes with dark precipitates | |
| Rifampin-susceptible (35) | Rifampin-resistant (10) | |
| 0 | 35 | 10 |
| 0.5 | 5 | 10 |
| 1.0* | 0 | 10 |
| 2.0 | 0 | 10 |
