The resistance to first-line drugs can increase the risk of treatment failure and development of resistance to other anti-TB drugs. In TB endemic settings, a considerable rate of recurrence cases exhibited each year which adds significant burden to the prevalence of disease worldwide.
A total of 562 sputum samples were collected from presumptive positive clinical cases of MDR tuberculosis. Treatment history and demographic data of the patients were obtained after informed consent. Xpert MTB/RIF assay was performed for simultaneous detection of MTB and rifampicin resistance. The mutation patterns of isoniazid and rifampicin were observed after multiplex PCR and reverse hybridization by Genotype® MTBDRplus version 2.0 assay.
A total of 73 among 97 cases (75.2%) of treatment failure were found positive for MDR-TB. Whereas, 79.6% newly diagnosed and 72.9% default cases were MDR in our isolates. The mutation of rpoB S531 L was slightly higher in new treatment cases (89.3%) as compared to the default (80.4%) and failure cases (84.8%). While, rpoB D516 V mutation was more prevalent in default cases (19.6%) with complete absence of rpoB 526 mutation which was observed in other two types of cases. The mutation pattern of katG resistance differed among drug naïve and recurrence cases. The resistance in newly diagnosed cases was mostly conferred by katG 315 (49.1%) whereas in default (70.8%) and failure cases (63.3%) isoniazid resistance was commonly associated with katG S315T1 mutation. Mutations in inhA promoter region occurred at nucleotide position -8 and -15. In new cases the rate of mutation of C-15 T was 3.7% and T-8A was 1.5% while in treatment failure cases the frequency for C-15 T and T-8C was 2.5 and 3.8% respectively. However, no inhA promoter region mediated mutations were detected in default treatment cases.
Retreated cases are at more risk of developing hot spot mutations. An unusual difference in mutation pattern was determined in naïve and recurrence cases. Some mutations were exclusively associated with the retreatment of anti-TB drugs which suggest the increased risk of resistance with poor treatment outcome.

Copyright © 2020. Published by Elsevier Ltd.

References

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