In Vitro Antibacterial Activity of Myxin Against <scp> <i>Mycobacterium abscessus</i> </scp>

Nontuberculous mycobacteria (NTM) infections, especially those caused by Mycobacterium abscessus, are extremely difficult to treat due to the organisms' intrinsic resistance to many antimicrobials. Myxin is a naturally occurring phenazine-5,10-dioxide antibiotic from Sorangium sp., notable for its broad-spectrum antimicrobial activity. In this study, we determined the susceptibilities of Myxin against 11 NTM reference strains and 194 clinical M. abscessus isolates using microdilution assays. Additionally, time-kill kinetic experiments were performed to distinguish the clearing efficiency of Myxin in broth. We also evaluated the efficacy of Myxin against intracellular M. abscessus in THP-1 macrophages. Checkerboard assays assessed the interactions between Myxin and eight clinically important anti-NTM antibiotics. Myxin demonstrated potent activity against M. abscessus with low MIC values (MIC₅₀ = 0.125 mg/L and MIC₉₀ = 0.5 mg/L). Treatment with 20 × MIC of Myxin in 7H9 broth resulted in up to 10 log₁₀ CFU/mL reduction after 4 days of incubation. An intracellular concentration-dependent bactericidal effect of Myxin was observed in THP-1 macrophages. Myxin exhibited no antagonism in combination with standard anti-NTM drugs. As such, Myxin represents a promising candidate for the treatment of M. abscessus and other NTM infections.