GSK1322322 is a novel peptide deformylase (PDF) inhibitor being developed for the intravenous and oral treatment of acute bacterial skin and skin structure infections and hospitalized patients with community-acquired pneumonia. The activity of GSK1322322 was tested against a global collection of clinical isolates of Haemophilus influenzae (n = 2,370), Moraxella catarrhalis (n = 115), Streptococcus pneumoniae (n = 947), Streptococcus pyogenes (n = 617), and Staphylococcus aureus (n = 940), including strains resistant to one or more marketed antibiotics. GSK1322322 had an MIC(90) of 1 μg/ml against M. catarrhalis and 4 μg/ml against H. influenzae, with 88.8% of β-lactamase-positive strains showing growth inhibition at that concentration. All S. pneumoniae strains were inhibited by ≤ 4 μg/ml of GSK1322322, with an MIC(90) of 2 μg/ml. Pre-existing resistance mechanisms did not affect its potency, as evidenced by the MIC(90) of 1 μg/ml for penicillin, levofloxacin, and macrolide-resistant S. pneumoniae. GSK1322322 was very potent against S. pyogenes strains, with an MIC(90) of 0.5 μg/ml, irrespective of their macrolide resistance phenotype. This PDF inhibitor was also active against S. aureus strains regardless of their susceptibility to methicillin, macrolides, or levofloxacin, with an MIC(90) of 4 μg/ml in all cases. Time-kill studies showed that GSK1322322 had bactericidal activity against S. pneumoniae, H. influenzae, S. pyogenes, and S. aureus, demonstrating a ≥ 3-log(10) decrease in the number of CFU/ml at 4× MIC within 24 h in 29 of the 33 strains tested. Given the antibacterial potency demonstrated against this panel of organisms, GSK1322322 represents a valuable alternative therapy for the treatment of infectious diseases caused by drug-resistant pathogens.