Abstract
ABSTRACTFor Mycobacterium tuberculosis complex (MTBC), the rapid and accurate diagnosis of drug resistance is crucial to ensure early initiation of appropriate therapy. Recently, a new molecular diagnostic test, the FluoroType MTBDR, aimed at detecting rifampin and isoniazid resistance has become available. This study aimed to evaluate the FluoroType MTBDR in comparison to phenotypic drug susceptibility testing (DST) using M. tuberculosis complex isolates. MTBC isolates underwent phenotypic DST and were tested using the FluoroType MTBDR and Genotype MTBDRplus. Sanger sequencing of the key regions of rpoB, katG, inhA, and aphC was performed for isolates with discordant phenotypic and molecular results. Furthermore, isolates with specific wild-type bands missing in the Genotype MTBDRplus, indicating the presence of a mutation, were investigated by Sanger sequencing. Specificity and sensitivity, defined as the proportions of isolates correctly determined as susceptible and resistant by the FluoroType MTBDR compared to phenotypic DST, were calculated. A total of 180 culture isolates were included; phenotypic DST showed 85 isolates susceptible to isoniazid and rifampin, 7 with isoniazid monoresistance, 7 with rifampin monoresistance, and 81 with multidrug resistance. The specificity of the FluoroType MTBDR was 100% (95% confidence interval [CI], 96.0 to 100%) for both rifampin and isoniazid. The sensitivity was 91.7% (95% CI, 83.6 to 96.6%) for isoniazid and 98.9% (95% CI, 93.8 to 100.0%) for rifampin. The FluoroType MTBDR has a high sensitivity and specificity for the detection of rifampin and isoniazid resistance when using culture isolates.
Highlights
Rapid and accurate laboratory diagnoses of Mycobacterium tuberculosis drug susceptibility and resistance are crucial to ensure early initiation of appropriate therapy, to adequately manage disease, and to control further transmission
This study aimed to compare the results of phenotypic drug susceptibility testing (DST), GenoType MTBDRplus, and FluoroType MTBDR using cultures positive for M. tuberculosis complex (MTBC)
Of the seven cultures falsely tested as INH susceptible by the FluoroType MTBDR, four had katG and/or inhA mutations detected by the Genotype MTBDRplus
Summary
Rapid and accurate laboratory diagnoses of Mycobacterium tuberculosis drug susceptibility and resistance are crucial to ensure early initiation of appropriate therapy, to adequately manage disease, and to control further transmission. The most widely used LPA, the GenoType MTBDRplus, detects the most prevalent mutations in the rpoB, katG, inhA genes. The FluoroType MTBDR, which is directed at the same target genes but uses a different technology, has been developed. This assay combines a linear-after-the-exponential PCR (LATE-PCR) [9] with special probes using lights-on/ lights-off detection technology [10]. The FluoroType MTBDR has several advantages over the Genotype MTBDRplus: (i) less hands-on time, (ii) more-rapid results, (iii) decreased risk of DNA contamination, and (iv) automatic interpretation with the possibility to import results directly into a laboratory information system. The sensitivity and specificity of this new method for detecting RMP and INH resistance have not been investigated under routine conditions
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