1353. In Vitro Activity of Lefamulin (LEF) Against Bacterial Pathogens Commonly Causing Community-Acquired Bacterial Pneumonia (CABP): 2016 SENTRY Data From the United States

BACKGROUND: LEF, the first pleuromutilin antibiotic for IV and oral use in humans, is in Phase 3 clinical trials for the treatment of CABP in adults. In the first of these to be completed, LEF demonstrated noninferiority to moxifloxacin ± linezolid. LEF inhibits bacterial translation by binding the 50S ribosomal subunit at the A- and P-sites in the peptidyl transferase center. CABP is a leading cause of infectious diseases in the United States and increasing antibacterial resistance complicates its treatment. This study investigated the in vitro activity of LEF and comparators against a contemporary set of bacterial respiratory pathogens collected in the United States. METHODS: Isolates (n = 1674, 1/patient) were collected from 32 medical centers in the United States as part of the SENTRY Surveillance Program. LEF and comparators were tested by CLSI broth microdilution methods, and susceptibility was determined using the CLSI (2018) breakpoints. RESULTS: LEF was the most active compound against Streptococcus pneumoniae (MIC(50/90) of 0.12/0.12 µg/mL), and its activity was not affected by resistance to other antibiotic classes. S. pneumoniae isolates were susceptible to levofloxacin (99.1%) and ceftriaxone (97.7%), whereas only 53.9%, 63.9%, and 80.4% of isolates were susceptible to macrolides, penicillin (oral), and tetracycline, respectively. LEF also showed potent activity against Staphylococcus aureus (MIC(50/90) of 0.06/0.12 µg/mL), including methicillin-resistant (MRSA) isolates (MIC(50/90) of 0.06/0.12 µg/mL, 87.1% resistant to erythromycin), Haemophilus influenzae, (MIC(50/90) of 0.5/1 µg/mL, 26.9% β-lactamase producing), and Moraxella catarrhalis (MIC(50/90) 0.06/0.06 µg/mL, 96.5% β-lactamase positive) (figure). [Image: see text] CONCLUSION: LEF displayed potent in vitro activity against a contemporary collection of respiratory pathogens from the United States. LEF was active regardless of resistance phenotype to other antibiotic classes including β-lactams, tetracyclines, or macrolides. These results further support the clinical development of lefamulin for the treatment of CABP or other respiratory tract infections. DISCLOSURES: S. Paukner, Nabriva: Employee and Shareholder, Salary. R. K. Flamm, Nabriva: Research Contractor, Research grant. S. P. Gelone, Nabriva Therapeutics: Employee, Equity, Shareholder and Salary. Achaogen: Shareholder, Equity, Shareholder. H. S. Sader, Nabriva Therapeutics: Research Contractor, Research support.