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.
Keywords: Antituberculous susceptibility testing; microdilution; nontuberculous mycobacteria; omadacycline; tedizolid.
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