7-Year (2015–21) longitudinal surveillance of lefamulin in vitro activity against bacterial pathogens collected worldwide from patients with respiratory tract infections including pneumonia and characterization of resistance mechanisms.

Objectives Lefamulin (Xenleta™), a pleuromutilin antibiotic, was approved for the oral and IV treatment of community-acquired bacterial pneumonia (CABP) in adults in 2019/2020. This study evaluated the in vitro activity of lefamulin and comparators against 19 584 unique bacterial isolates collected from patients with community-acquired respiratory tract infections and hospitalized patients with pneumonia within the global SENTRY Antimicrobial Surveillance Program during 2015–21. Methods Isolates were susceptibility tested by the CLSI broth microdilution method, and resistance mechanisms were investigated in isolates with elevated lefamulin MICs. Results Lefamulin exhibited potent antibacterial activity against the most common and typical CABP pathogens tested, including Streptococcus pneumoniae [MIC50/90, 0.06/0.25 mg/L; 99.9% susceptible (S)], Staphylococcus aureus (MIC50/90, 0.06/0.12 mg/L; 99.6% S), Haemophilus influenzae (MIC50/90, 0.5/2 mg/L; 99.1% S) and Moraxella catarrhalis (MIC50/90, 0.06/0.12 mg/L; 100.0% S). Potent activity was also observed against the less common pneumonia pathogens: β-haemolytic (MIC50/90 of 0.03/0.06 mg/L) and viridans group Streptococcus spp. (MIC50/90 of 0.06/0.25 mg/L) and Haemophilus parainfluenzae (MIC50/90 of 1/4 mg/L). Lefamulin's activity was not adversely affected by resistance to macrolides, penicillin, tetracyclines, fluoroquinolones and other resistance phenotypes. Non-susceptibility/resistance to lefamulin was rare and primarily determined by ribosomal protection through vga (A) variants in S. aureus, overexpression of AcrAB-TolC efflux pump in H. influenzae or modifications in L3, L4 and 23SrRNA in Streptococcus spp. Conclusions Based on the coverage of the most important CABP pathogens and lacking cross-resistance, lefamulin may represent a valuable empirical treatment option for ambulatory and hospitalized patients with CABP, particularly in settings with high prevalence of resistance. [ABSTRACT FROM AUTHOR]