Background: The antimicrobial activities of some new oxazolidinones against slowly growing mycobacteria (SGM) have never been well evaluated.
Methods: We evaluate the in vitro susceptibility of 20 reference strains and 157 clinical isolates, pertaining different SGM species, against four oxazolidinones, ie, delpazolid, sutezolid, tedizolid and linezolid. In addition, the association of linezolid resistance and mutations in 23srRNA, rplC, rplD  were also tested.
Results: Sutezolid presented the strongest antimicrobial activity against the clinical isolates of M. intracellulare  than the other oxazolidinones, with MIC₅₀ at 2 μg/mL and MIC₉₀ at 4 μg/mL. MICs of sutezolid were usually 4- to 8-fold lower than these of linezolid against M. intracellulare  and M. avium . The tested isolates of M. kansasii  were susceptible to all of the four oxazolidinones. According to the multiple sequence alignment, novel 23srRNA  mutations (A2267C and A2266G) in M. intracellulare  and rplD  mutations (Thr147Ala) in M. avium  were identified in this study which have plausible involvement in rendering resistance against linezolid.
Conclusion: This study showed that sutezolid harbors the strongest inhibitory activity against M. intracellulare, M. avium  and M. kansasii  in vitro, which provided important insights on the potential clinical application of oxazolidinones for treating SGM infections.
Keywords: slowly growing mycobacteria, delpazolid, sutezolid, tedizolid, linezolid, antimicrobial activity