Resazurin microtitre plate assay and Sensititre® MycoTB for detection of Mycobacterium tuberculosis resistance in a high tuberculosis resistance setting

Background: Rapid diagnosis of drug-resistant Mycobacterium tuberculosis is a challenge in low-income countries. Phenotypic drug susceptibility testing using Sensititre (R) MycoTB assay and the resazurin microtitre plate assay (REMA) are relatively new innovative methods to determine drug susceptibility. Objectives: This study aimed to determine the performance of the Sensititre and REMA for M. tuberculosis drug susceptibility testing in a high-volume tuberculosis reference laboratory. Methods: A laboratory-based study was performed at the Inkosi Albert Luthuli Central Hospital Tuberculosis Laboratory from January 2014 to June 2015. The Sensititre (R) MycoTB plate and REMA were compared to the gold standard agar proportion method (APM) using 134 stored isolates. Results: Agreement between the Sensititre (R) MycoTB plate and APM was observed with 98% sensitivity, 82% specificity, 94% positive and 93% negative predictive values of the Sensititre (R) MycoTB assay for the detection of rifampicin resistance and 97%, 96%, 99% and 88% for isoniazid resistance. Good categorical agreement between the REMA and the APM was observed among isolates with 89% sensitivity, 68% specificity, 89% positive and 68% negative predictive value for the detection of rifampicin resistance and 95%, 96%, 99% and 81% for isoniazid resistance. Results for the second-line drugs showed elevated minimum inhibitory concentrations for multidrug-resistant and extensively drug-resistant tuberculosis isolates. Conclusion: The REMA and Sensititre (R) MycoTB plate are attractive alternatives to the gold standard A PM for the phenotypic detection of M. tuberculosis drug resistance.