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

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.

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.

Among 9369 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.

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.