The detection of drug resistant mutations in mycobacterium tuberculosis strains using anyplex MTB/NTM/MDR-TB plus assay in Limpopo Province

Abstract

Introduction: Multidrug-resistant tuberculosis (MDR-TB) caused by resistance to at least rifampicin (RIF) and isoniazid (INH) drugs is a growing public health concern in South Africa. The detection of MDR-TB still relies on culture despite advancement in molecular diagnostic technology. Currently MTBDRplus and GeneXpert are the only available assays used in rapid diagnosis of MDR-TB using chromosomal mutations in drug target regions. Some strains are missed by these assays due to their limitation in mutational detection profile. Novel Seegene Anyplex assays simultaneously detect TB and resistance to RIF and INH using fifteen and six mutational probes, respectively within 3 hours. Limpopo Province has limited information on the circulating strains of TB. Aim: To determine drug-resistant Mycobacterium tuberculosis (M. tuberculosis) mutations using Anyplex™ MTB/NTM/MDR-TB real time assay and characterise the drug-resistant strains. Methods: We prospectively collected 204 clinical samples at Modimolle MDR-TB unit and retrospectively used 104 culture isolates from MRC laboratory in Pretoria. The MTBDRplus assay was used to screen for M. tuberculosis and drug resistant mutations to RIF and INH drugs. Anyplex™ MTB/NTM/MDR-TB assay was used for rapid detection of M. tuberculosis and drug resistance to RIF and INH within 3 hours. The discordance between phenotypic and genotypic assays was resolved by sequencing and the Anyplex™ resistant profiles were spoligotyped. Diagnostic data was collected from NHLS and MRC databases and analysed using the Microsoft excel and Epi Info version 3.5. Descriptive statistics (percentages and frequencies) were used to explain proportions. Results: The Anyplex™ MTB/NTM assay detected M. tuberculosis in 69/111(62%) and 100/104 (96%) of clinical and culture samples respectively. The sensitivities, specificity, PPV and NPV obtained for both RIF and INH resistance by Anyplex™ MDR-TB assay were 67%, 59%, 67%, 55% and 15%, 100%, 100% and 17%, respectively. Anyplex™ MTB/NTM/MDR-TB resolved 23/45 (51%) of discordant vi samples. Sequencing of remaining discordant isolates revealed L511P, L533P and D516Y mutations within rpoB gene. A novel R385W mutation within katG was also detected. Spoligotyping of Anyplex™ MDR-TB resistant clinical isolates revealed Euro American clade with 20% followed by 15% Manu2, 5% East African Indian, 5% H37Rv, 5% atypical and 50% were orphans. Conclusion: The novel Anyplex™ MTB/NTM/MDR-TB assay is a rapid and valid technique for detecting M. tuberculosis and most common mutations conferring resistance to RIF and INH. However further investigations are required, as the assay has a lower sensitivity as compared to already endorsed techniques.