Investigation of in vitro efficacy of new generation drugs tedizolid and omadacycline against nontuberculous mycobacteria

Abstract

Background: Species‑specific antimicrobial susceptibility testing is crucial for the effective treatment of nontuberculous mycobacteria (NTM). In this study, the in vitro antimicrobial activities of two next‑generation antibacterial agents, tedizolid (TZD) and omadacycline (OMC) – which have demonstrated strong in vitro activity against NTM species but have not been comprehensively evaluated for NTM treatment in Turkiye – were investigated. Methods: In this study, antibiotic susceptibility testing for TZD and OMC was performed on a total of 104 NTM isolates (59 rapid‑growing and 45 slow‑growing) using the colorimetric microdilution method, in accordance with Clinical and Laboratory Standards Institute (CLSI) M24 and M62 standards. Minimum inhibitory concentration (MIC) ranges were 0.015–32 µg/ml for TZD and 0.003–64 µg/ml for OMC. For the interpretation of TZD susceptibility, the CLSI M62 breakpoints established for linezolid were used (≤8 µg/ml: susceptible, 16 µg/ml: intermediate, and ≥32 µg/ml: resistant). Results: Among the rapidly growing NTM isolates, only one Mycobacterium fortuitum isolate was found to be intermediate (1/29; 16 µg/mL), while one Mycobacterium avium isolate among the slowly growing species was classified as resistant (1/6; ≥32 µg/mL). The remaining 102 isolates were all found to be susceptible to TZD (≤8 µg/mL). Since no standardized breakpoint has yet been established for OMC, only the observed MIC values were reported. Conclusions: The findings demonstrated that TZD exhibits strong in vitro activity against NTM isolates, whereas OMC showed a variable activity profile, particularly among rapidly growing species. These results support the necessity of basing antibiotic selection for the treatment of NTM infections on species‑specific susceptibility testing.