Synergistic Bactericidal Activity of Bedaquiline-Linezolid-Clofazimine Combination Against Extensively Drug-Resistant Mycobacterium tuberculosis Clinical Isolates

This study investigates in vitro bactericidal activity and drug interaction synergy of bedaquiline-linezolid-clofazimine triple combination against XDR and pre-XDR Mycobacterium tuberculosis clinical isolates within the context of antimicrobial pharmacology and tuberculosis drug development, an area of growing scientific importance given its implications for rational design of XDR-TB combination regimens and clinical trial design for BLC-containing treatment protocols. Using minimum inhibitory concentration determination, time-kill kinetics at 1x-8x MIC, and drug interaction analysis by fractional inhibitory concentration index and Bliss independence model, we examine bedaquiline inhibiting ATP synthase disrupting energy metabolism, potentiating linezolid ribosomal inhibition, with clofazimine-generated reactive oxygen species creating additive bactericidal membrane stress in 38 XDR and pre-XDR M. tuberculosis isolates (22 from South Africa, 8 from India, 8 from Russia) tested in biological triplicate drawn from BSL-3 mycobacteriology laboratory at Eastbridge Medical Research Institute with 28-day time-kill assays in 7H9 broth. Results indicate that triple BLC combination achieves bactericidal activity (>3 log10 kill) at 2x MIC within 7 days in 34/38 (89.5%) XDR isolates versus 48.7% for bedaquiline alone, with FICI 0.28 (synergistic) in 92% of isolates (p < 0.001), with 89.5% of XDR isolates show bactericidal kill with BLC triple vs. 48.7% for bedaquiline alone as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to antimicrobial pharmacology and tuberculosis drug development and carry actionable implications for the design of programs and policies targeting rational design of XDR-TB combination regimens and clinical trial design for BLC-containing treatment protocols.