In Vitro Susceptibility Testing of Tedizolid against Isolates of Nocardia.

There is a paucity of efficacious antimicrobials (especially oral) against clinically relevant species of Nocardia. To date, all species of Nocardia have been susceptible to linezolid, the first commercially available oxazolidinone. Tedizolid is a new oxazolidinone with previously reported improved in vitro and in vivo (intracellular) potency against multidrug-resistant strains of Mycobacterium sp. and Nocardia brasiliensis. Using the current Clinical and Laboratory Standards Institute-recommended broth microdilution method, 101 isolates of Nocardia spp., including 29 Nocardia cyriacigeorgica, 17 Nocardia farcinica, 13 Nocardia nova complex, 21 Nocardia brasiliensis, 5 Nocardia pseudobrasiliensis, and 5 Nocardia wallacei isolates and 11 isolates of less common species, were tested for susceptibility to tedizolid and linezolid. For the most common clinically significant species of Nocardia, tedizolid MIC50 values were 0.25 mu g/ml for N. nova complex, N. brasiliensis, N. pseudobrasiliensis, and N. wallacei, compared to linezolid MIC50 values of 1, 2, 0.5, and 1 mu g/ml, respectively. Tedizolid and linezolid MIC90 values were 2 mu g/ml for N. nova complex and N. brasiliensis. Tedizolid MIC50 and MIC90 values for both N. cyriacigeorgica and N. farcinica were 0.5 mu g/ml and 1 mu g/ml, respectively, compared to linezolid MIC50 and MIC90 values of 2 and 4 mu g/ml, respectively. Based on MIC90 values, this study showed that tedizolid was 2-to 3-fold more active than linezolid in vitro against most common species of Nocardia, with the exception of the N. nova complex and N. brasiliensis, for which values were the same. These results may warrant evaluation of tedizolid as a potential treatment option for Nocardia infections.