Revisiting the susceptibility testing of Mycobacterium tuberculosis to ethionamide in solid culture medium.
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Date
2015-11
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Abstract
Background & objectives: Increase in the isolation of drug resistant phenotypes of Mycobacterium tuberculosis necessitates accuracy in the testing methodology. Critical concentration defining resistance for ethionamide (ETO), needs re-evaluation in accordance with the current scenario. Thus, re-evaluation of conventional minimum inhibitory concentration (MIC) and proportion sensitivity testing (PST) methods for ETO was done to identify the ideal breakpoint concentration defining resistance.
Methods: Isolates of M. tuberculosis (n=235) from new and treated patients were subjected to conventional MIC and PST methods for ETO following standard operating procedures.
Results: With breakpoint concentration set at 114 and 156 μg/ml, an increase in specificity was observed whereas sensitivity was high with 80 μg/ml as breakpoint concentration. Errors due to false resistant and susceptible isolates were least at 80 μg/ml concentration.
Interpretation & conclusions: Performance parameters at 80 μg/ml breakpoint concentration indicated significant association between PST and MIC methods.
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Keywords
Drug resistance, ethionamide, MIC method, Mycobacterium tuberculosis, proportion sensitivity testing
Citation
Rajagopalan Lakshmi, Ramachandran Ranjani, Kumar D Ravi, Sundar A Syam, Radhika G, Rahman Fathima, Selvakumar N, Kumar Vanaja. Revisiting the susceptibility testing of Mycobacterium tuberculosis to ethionamide in solid culture medium. Indian Journal of Medical Research. 2015 Nov; 142(5): 538-542.