In Vitro Susceptibility Testing of Tedizolid against Nontuberculous Mycobacteria

Tedizolid is a new oxazolidinone with improvedin vitro and intracellular potency againstMycobacterium tuberculosis , including multidrug-resistant strains, and some species of nontuberculous mycobacteria (NTM) compared with that of linezolid. Using the current Clinical and Laboratory Standards Institute (CLSI)-recommended method of broth microdilution, susceptibility testing of 170 isolates of rapidly growing mycobacteria showed equivalent or lower (1- to 8-fold) MIC50 and/or MIC90 values for tedizolid compared with that for linezolid. The tedizolid MIC90 values for 81 isolates ofM. abscessus subsp.abscessus and 12 isolates ofM. abscessus subsp.massiliense were 8 μg/ml and 4 μg/ml, respectively, compared with linezolid MIC90 values of 32 μg/ml for both. The MIC90 values for 20 isolates ofM. fortuitum were 2 μg/ml for tedizolid and 4 μg/ml for linezolid. Twenty-two isolates ofM. chelonae had tedizolid and linezolid MIC90 s of 2 μg/ml and 16 μg/ml, respectively. One hundred forty-two slowly growing NTM, including 7/7M. marinum , 7/7M. kansasii , and 7/11 of other less commonly isolated species, had tedizolid MICs of ≤1 μg/ml and linezolid MICs of ≤4 μg/ml. One hundred isolates ofMycobacterium avium complex and eightM. simiae isolates had tedizolid MIC50 s of 8 μg/ml and linezolid MIC50 s 32 and 64 μg/ml, respectively. NineM. arupense isolates had MIC50 s of 4 μg/ml and 16 μg/ml for tedizolid and linezolid, respectively. These findings demonstrate a greaterin vitro potency of tedizolid than linezolid against NTM and suggest that an evaluation of tedizolid as a potential treatment agent for infections caused by selected NTM is warranted.