Lefamulin, also known as BC-3781, is a semi-synthetic compound that inhibits the synthesis of bacterial protein, which is required for bacteria to grow. Lefamulin acts by binding to the peptidyl transferase center, or PTC, on the bacterial ribosome in such a way that it interferes with the interaction of protein production at two key sites known as the “A” site and the “P” site, resulting in the inhibition of bacterial proteins and the cessation of bacterial growth. Lefamulin’s binding occurs with high affinity, high specificity and at molecular sites that are different than other antibiotic classes. Lefamulin exhibited MIC50 and MIC90 values of 0.12 and 0.25 μg/ml, respectively, against the entire collection (n = 822). Similar results were obtained for lefamulin against each of the most common serotypes as well as against multidrug-resistant isolates and strains that are nonsusceptible to ceftriaxone or erythromycin. Lefamulin may be useful for the treatment of community-acquired respiratory tract infections.