Abstract
Early detection of drug resistance in Mycobacterium tuberculosis isolates allows for earlier and more effective treatment of patients. The aim of this study was to investigate the performance of the malachite green decolourisation assay (MGDA) in detecting isoniazid (INH) and rifampicin (RIF) resistance in M. tuberculosis clinical isolates. Fifty M. tuberculosis isolates, including 19 multidrug-resistant, eight INH-resistant and 23 INH and RIF-susceptible samples, were tested. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and agreement of the assay for INH were 92.5%, 91.3%, 92.5%, 91.3% and 92%, respectively. Similarly, the sensitivity, specificity, PPV, NPV and agreement of the assay for RIF were 94.7%, 100%, 100%, 96.8% and 98%, respectively. There was a major discrepancy in the tests of two isolates, as they were sensitive to INH by the MGDA test, but resistant by the reference method. There was a minor discrepancy in the tests of two additional isolates, as they were sensitive to INH by the reference method, but resistant by the MGDA test. The drug susceptibility test results were obtained within eight-nine days. In conclusion, the MGDA test is a reliable and accurate method for the rapid detection of INH and RIF resistance compared with the reference method and the MGDA test additionally requires less time to obtain results.
Highlights
Detection of drug resistance in Mycobacterium tuberculosis isolates allows for appropriate and timely treatment (Martin et al 2008)
Two isolates were sensitive to INH by the malachite green decolourisation assay (MGDA) test, but resistant by the reference method
Two additional isolates were sensitive to INH by the reference method, but resistant by the MGDA test
Summary
Detection of drug resistance in Mycobacterium tuberculosis isolates allows for appropriate and timely treatment (Martin et al 2008). The proportion method, performed on Löwenstein-Jensen and 7H10 or 7H11 agar media, is recommended as a reference method. This method requires at least three-six weeks to obtain results (Kent & Kubica 1985). There are rapid automated systems for drug susceptibility testing. The BACTEC 460TB system (Becton Dickinson Diagnostic Systems, Sparks, MD, USA), which is no longer commercially available, is a semi-automated rapid system that is expensive and contains radioactive material. The BACTEC MGIT 960 system (Becton Dickinson Diagnostic Systems) is a non-radiometric rapid automated system. The aim of this study was to investigate the performance of the MGDA test for the detection of isoniazid (INH) and rifampicin (RIF) resistance in M. tuberculosis clinical isolates
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