Lefamulin harbors promising anti-tuberculosis activity against multidrug-resistant Mycobacterium tuberculosis isolates.

Multidrug-resistant tuberculosis (MDR-TB) is often associated with poor clinical outcomes. This study evaluated the in vitro activity of lefamulin (LEF) and intracellular activities against Mycobacterium tuberculosis. In this study, we evaluated the potential of LEF as a new drug candidate for treating M. tuberculosis infections, including MDR-TB. The antimicrobial susceptibility testing was performed to determine the minimum inhibitory concentrations (MICs) of LEF against 132 clinical isolates of M. tuberculosis. The intracellular activity of LEF and its interaction with other anti-tuberculosis drugs were also evaluated using M. tuberculosis H37Rv. From the 132 M. tuberculosis clinical isolates, the MIC₅₀ and MIC₉₀ were 0.5 µg/mL and 1 µg/mL, respectively. The tentative epidemiological cut-off (ECOFF) against LEF was defined at 1 µg/mL. After 5 days of incubation, LEF at 2 µg/mL inhibited 89.88% ± 1.73% of intracellular bacterial growth, which was comparable with the inhibitory rate of 94.29% ± 1.32% achieved by INH at 2 µg/mL. In addition, a synergy between LEF and bedaquiline (BDQ) was observed with a fractional inhibitory concentration index = 0.5. Furthermore, LEF showed no correlation with resistance to 10 anti-tuberculosis drugs. The minimum bactericidal concentration/MIC of LEF values suggested that it is a bacteriostatic drug against M. tuberculosis, and the bactericidal activity is mainly characterized by a concentration-dependent pattern. LEF has potent inhibitory activities against M. tuberculosis in vitro as well as in macrophages. Furthermore, the synergistic effect with BDQ also favors LEF as a promising drug candidate for tuberculosis treatment, especially for MDR-TB.IMPORTANCELefamulin (LEF), the first systemic pleuromutilin antibiotic approved for human use, exhibits broad-spectrum activity against Gram-positive bacteria. However, its in vitro activity against Mycobacterium tuberculosis (Mtb) remains unexplored. This study evaluated the potential of LEF for treating Mtb infections, including multidrug-resistant tuberculosis. Our findings demonstrate that LEF possesses potent bacteriostatic activity against Mtb in vitro and exhibits synergistic effects when combined with bedaquiline. These results suggest LEF as a promising therapeutic candidate for tuberculosis treatment.