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

ABSTRACT 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 MIC 50 and MIC 90 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. IMPORTANCE Lefamulin (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.