LAUSR

Abstract Background Delafloxacin (DLX) is a broad-spectrum fluoroquinolone (FQ) antibacterial that has completed clinical development (oral and intravenous formulations) with the new drug application currently under the Food and Drug Administration review for the treatment of acute bacterial skin and skin structure infections (ABSSSI). DLX is also in clinical trials for community-acquired bacterial pneumonia. In this study, in vitro susceptibility results for DLX and comparator agents were determined for clinical isolates from community-acquired respiratory tract infections (CA-RTI) collected in medical centers in the United States and Europe participating in the SENTRY surveillance program during 2014–2016. Methods A total of 3,093 isolates that included 1,673 Streptococcus pneumoniae (SPN), 805 Haemophilus influenzae (HI) and 555 Moraxella catarrhalis (MC) were collected during 2014–2016 and included only 1 isolate/patient/infection episode. Isolate identifications were confirmed at JMI Laboratories. Susceptibility testing was performed according to CLSI reference broth microdilution methodology, and results were interpreted per CLSI (2017) breakpoints. Other antibacterials tested included levofloxacin (LVX) and penicillin. Β-lactamase production for HI and MC was determined by the nitrocephin disk test. Results DLX demonstrated potent in vitro activity against SPN (MIC50/90 0.015/0.03 mg/L). Activity remained the same for penicillin-intermediate or -resistant isolates. For 23 LVX nonsusceptible SPN, the DLX MIC50/90 were 0.12/0.25 mg/L with all isolates having DLX MIC values ≤1 mg/L. For HI, the DLX MIC50/90 were ≤0.001/0.004 mg/L, and for MC the MIC50/90 were 0.008/0.008 mg/L. DLX activity was unaffected by the presence of β-lactamase for either HI or MC. Activity of DLX was similar for US and European isolates. Conclusion Delafloxacin demonstrated potent in vitro antibacterial activity against CA-RTI pathogens, including SPN, HI, and MC. These data support the continued study of DLX as a potential treatment for community-acquired pneumonia. Disclosures D. Shortridge, Melinta Therapeutics: Research Contractor, Research grant; J. M. Streit, Melinta Therapeutics: Research Contractor, Research grant; M. D. Huband, Melinta Therapeutics: Research Contractor, Research grant; P. R. Rhomberg, Melinta Therapeutics: Research Contractor, Research grant; R. K. Flamm, Melinta Therapeutics: Research Contractor, Research grant