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

Area of Science:

• Microbiology
• Infectious Diseases
• Clinical Diagnostics

Background:

• Moxifloxacin-resistant tuberculosis treatment is challenging due to heteroresistance and genotype-phenotype discordance.
• Accurate minimum inhibitory concentration (MIC)-based drug susceptibility testing (DST) is crucial for effective tuberculosis therapy.
• Optimizing treatment regimens requires reliable DST methods for moxifloxacin.

Purpose of the Study:

• To compare moxifloxacin MICs in pre-extensively drug-resistant tuberculosis (pre-XDR-TB) isolates.
• To evaluate the Sensititre MYCOTB AST plate against the BACTEC MGIT 960 reference method.
• To assess the diagnostic accuracy and agreement of the Sensititre MYCOTB AST plate for moxifloxacin DST.

Main Methods:

• A prospective laboratory-based comparative study was conducted in central India.
• Leftover patient samples with second-line drug resistance were cultured and isolates were tested.
• Isolates were tested using BACTEC MGIT 960 and Sensititre MYCOTB AST with blinded interpretation.

Main Results:

• The Sensititre MYCOTB AST plate demonstrated 100% sensitivity and 66.7% specificity for moxifloxacin DST.
• Overall accuracy was 96.75% with substantial agreement (Cohen's kappa = 0.783) with the MGIT 960 method.
• The index test offered quantitative MIC ranges, shorter turnaround times, and a simplified workflow.

Conclusions:

• Good concordance was observed between the Sensititre MYCOTB AST plate and the MGIT 960 for moxifloxacin DST.
• The Sensititre MYCOTB AST plate shows potential for routine DST and MIC-guided management of pre-XDR-TB.
• Operational simplicity and ability to capture MIC variability support the use of this method.