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In Vitro Activity of Tedizolid and Omadacycline in Nontuberculous Mycobacteria

S Turkkal(1) N E Ozcatalkaya(1) E Ciftci(1) G Yaman(2) D Satana(3)

1:Istanbul University, Institute of Health Science, Department of Medical Microbiology; 2:Maltepe University, Faculty of Medicine, Department of Medical Microbiology; 3:Istanbul University, Istanbul Faculty of Medicine, Department of Medical Microbiology

Nontuberculous mycobacteria (NTM) are opportunistic pathogens found everywhere, especially in soil and water sources. In order to establish appropriate drug regimens against NTM infections, antibiotic susceptibility tests must be performed. In this study, the antimicrobial susceptibilities of a total of 105 NTM strains, including 64 rapid-growing and 41 slow-growing strains, to tedizolid and omadacycline were investigated using the colorimetric microdilution method according to CLSI M24 and M62 guidelines. The MIC range of 0.015-32 µg/ml was used for tedizolid and 0.003-64 µg/ml for omadacycline. Based on literature information, the critical concentration values recommended for linezolid in CLSI M62 (≤8 µg/ml susceptible; 16 µg/ml intermediate; ≥32 µg/ml resistant) were used to evaluate the susceptibility of tedizolid. Only one rapid-growing strain, M. fortuitum, was found to be intermediate (1/29; 16 µg/ml) to tedizolid, and one slow-growing strain, M. avium, was found to be resistant (1/6; ≥32 µg/ml), while all other NTM strains were susceptible (103/105; ≤8 µg/ml). As there is no recommended critical concentration value for omadacycline, only the MIC values obtained were reported for this antibiotic. The obtained MIC values are shown in the attached table. This study demonstrates that tedizolid has a strong in vitro effect on NTM, but omadacycline gives variable results on NTM strains, indicating that species-specific antimicrobial susceptibility testing is necessary to establish NTM treatment regimens.

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