Use of alamar blue assay as a colorimetric method for detection of multidrug-resistant Mycobacterium tuberculosis

In recent years, tuberculosis (TB) has acquired a growing importance in developed and developing countries. The spread of multidrug-resistant (MDR) strains of Mycobacterium tuberculosis is an increasing public health concern in many parts of the world, especially in low- income countries. Standard methods for drug susceptibility testing of M. tuberculosis are time-consuming. In this study, we have evaluated the possibility of using colorimetric method by means of Alamar Blue, to detect susceptibility of M. tuberculosis strains as less expensive and easier-to-read methods. For this study 23 isolates of Mycobacterium tuberculosis were obtained from Iranian National Research Institute of Tuberculosis and Long Diseases. 11 isolates were resistant to rifampin and isoniazid and 12 isolates were susceptible to rifampin and isoniazid. The colorimetric method in this study was performed with a critical concentration of 0.2 µg/ml for isoniazid and 2 µg/ml for rifampin in 7H9GC broth. The tubes were incubated at 37˚C for 4 weeks. For both rifampin and isoniazid, the sensitivity and specificity of Alamar Blue method was %100 and %90 respectively. In this study, the results for Alamar Blue were available in average 6 days. Medical laboratories in developing countries have to adapt a simple method, which does not require expensive equipment materials. In conclusion, this colorimetric method is simple, reliable and inexpensive methods to evaluate drug susceptibility of Mycobacterium tuberculosis, especially in laboratories with low- income. In this regard, Alamar Blue culture tubes have the optional to become the method of choice for assessing drug susceptibility of M. tuberculosis in countries like Iran.