Comparison of Sensititre MYCOTB MIC plate and the BACTEC MGIT SIRE kit for the detection of isoniazid resistance in Mycobacterium tuberculosis
(2017) ECCMID 2017 — Location: Vienne (22.April.2017)
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- Background: Multi-Drug Resistant Tuberculosis (MDR-TB) is defined as the association of rifampicin (RIF) and isoniazid (INH) resistance. Compared to RIF resistance which can be accurately detected using molecular assays targeting a 81bp of the rpoB gene, INH resistance is caused by a larger number of genetic mutations, and therefore phenotypic testing still remains the gold standard. We compared the analytical performance of the MYCOTB MIC plate (Trek Diagnostic Systems, Cleveland, OH) with the SIRE MGIT antimycobacterial susceptibility testing method (Becton, Dickinson and Co., Sparks, MD). Material/methods: We tested 14 Mycobacterium tuberculosis complex strains, including the fully susceptible reference strain H37Rv with both MYCOTB MIC plate and MGIT SIRE methods. In regard to the latter technique, INH was tested with both 0.1 μg/ml and 0.4 μg/ml concentrations. Sequencing of katG and inhA genes were performed in parallel. Results: Among the 14 strains tested, 10 were resistant to INH according to the MGIT SIRE and the MYCOTB MIC plate test. For 12/14 strains, all methods gave concordant results, including for INH level of resistance, which is supposed to be higher when a katG is involved. We found one discordant result, for which MGIT SIRE method was susceptible and the MYCOTB MIC plate reported a minimum inhibitory concentration (MIC) >4 μg/ml. For this strain, sequencing did not report a resistance mutation in the katG or the inhA genes. One strain was found resistant with both phenotypic methods, but was not associated with a katG or inhA mutation. Conclusions: We evaluated the Sensititre MYCOTB MIC plate as a potential tool for detecting INH resistance together with other drugs. We found an acceptable correlation with the MGIT SIRE method among the resistant strains, but we nevertheless observed a probable false resistant result linked to the MYCOTB MIC method. Based on these preliminary results, we did not modify our existing workflow procedures in clinical routine. More evaluation is still needed.
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Kaisergruber, J., BRESSANT, F., Colmant, A., Goeminne, L., Martin, A., Simon, A., & André, E. (2017). Comparison of Sensititre MYCOTB MIC plate and the BACTEC MGIT SIRE kit for the detection of isoniazid resistance in Mycobacterium tuberculosis. ECCMID 2017, Vienne. https://hdl.handle.net/2078.5/182330