Abstract
Genotype MTBDRsl Version 1 (V1.0) was recommended as an initial test for rapid detection of pre-extensively drug resistant (pre-XDR) and extensively drug resistant tuberculosis (XDR-TB). However, in recent years a number of novel mutations are identified that confer resistance. Thus, Genotype MTBDRsl V2.0 was endorsed by WHO. Though, Genotype MTBDRsl V2.0 has been rolled out in national TB programme in 2018, there is dearth of data from India on its performance for second line drug susceptibility testing (DST). For this, performance of new version was evaluated on 113 MDR-TB isolates. The results showed that 39 (34.5%) of these isolates were resistant to FQ and 7 (6.2%) were XDR by Genotype MTBDRsl V2.0. Amongst the FQ resistant isolates most prevalent mutation was ΔWT3-D94G (17; 38.6%) and N538D (12; 85.7%). Among the AG/CP and KAN resistant isolates most common mutation in the rrs region was ΔWT1-A1401G (5; 71.4%) and C-14T (2; 28.5%) in eis gene. Second line Bactec MGIT-960 detected 40 (35.4%) isolates as resistant to FQ and 6 (5.3%) as XDR isolates, whereas Genotype MTBDRsl V1.0 also detected 39 (34.5%) as resistant to FQ but missed 2 isolates in correctly identifying as XDR (5; 4.4%). Thus, concordance of second line Bactec MGIT-960 with Genotype MTBDRsl V2.0 was similar (100%) for FQ detection but it has improvised the diagnostic sensitivity for correctly identifying XDR isolates. Nevertheless, the cost of Genotype MTBDRsl V2.0 remains an issue for screening of second line drug (SLDs) resistance from countries with high burden of MDR-TB.
Highlights
Increasing resistance towards second line drugs (SLD’s) is a major global threat leading to preXDR and XDR-TB which has high mortality rates due to limited treatment options and lower rates of treatment success [1,2]
As probes for mutations associated with gyrB and eis genes were not included in Genotype MTBDRsl V1.0 resulting in lower sensitivity of the test
This study was performed on 113 MDR-TB isolates which were already tested for Genotype MTBDRsl V1.0 and Bactec MGIT-960 as published previously [7]
Summary
Increasing resistance towards second line drugs (SLD’s) is a major global threat leading to preXDR and XDR-TB which has high mortality rates due to limited treatment options and lower rates of treatment success [1,2]. Mutations in promotor region of eis gene for conferring low-level KAN mutations which is known to increase sensitivity of phenotypic KAN resistance by 9% has been reported [13]. Frequency of these mutations among pre-XDR and XDR-TB cases from India remains unknown. As probes for mutations associated with gyrB and eis genes were not included in Genotype MTBDRsl V1.0 resulting in lower sensitivity of the test. This study was planned in order to compare the usefulness of line probe assay (Genotype MTBDRsl V2.0) for detection of additional mutations in gyrB and eis genes over Genotype MTBDRsl V1.0 in comparison to Bactec MGIT-960 DST from India
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