Decoding moxifloxacin resistance in pre-XDR tuberculosis using MGIT 960 and MYCOTB AST

BACKGROUND AND OBJECTIVES: Treatment of moxifloxacin-resistant tuberculosis is complicated by heteroresistance, high resistance prevalence, genotype-phenotype discordance, pharmacokinetic antagonism, and the need for individualised regimen design. Reliable minimum inhibitory concentration (MIC)-based drug susceptibility testing (DST) is therefore essential for optimised therapy. This study aimed to compare moxifloxacin MICs in pre-extensively drug-resistant tuberculosis isolates using the BACTEC MGIT 960 as the reference method and Sensititre MYCOTB AST plate as the index test. METHODS: The prospective laboratory-based comparative study collected leftover routine patient samples, processed them for culture, and retrieved the isolates from BACTEC MGIT tubes that showed second-line drug resistance by line probe assay (LPA), and subsequently included them at the tertiary care centre in central India from July 2025 to February 2026. Non-tuberculous mycobacteria and samples with insufficient information were neglected. Eligible isolates were tested using MGIT 960 and Sensititre MYCOTB AST with blinded interpretation. Diagnostic accuracy and agreement were assessed. RESULTS: Among 9,369 samples screened,30 pre-XDR tuberculosis isolates met the inclusion criteria. For moxifloxacin DST, Sensititre MYCOTB AST demonstrated 100% sensitivity, 66.7% specificity, 96.75% overall accuracy, and substantial agreement with MGIT 960 (Cohen's kappa 0.783). The index test also provided quantitative MIC ranges, shorter turnaround time, low resource requirements, and a simplified workflow. CONCLUSION: Good concordance for moxifloxacin DST was observed between the methods. Its potential value in regular DST and MIC-guided management of pre-XDR-TB is supported by its operational simplicity and ability to capture MIC variability.