Introduction. Infections attributable to carbapenem-resistant Gram-negative bacilli are increasing globally. New antimicrobial agents are urgently needed to treat patients with these infections.Aim. To describe susceptibility to the novel carbapenem-β-lactamase inhibitor combination imipenem-relebactam and comparators of clinical isolates of non-Proteeae Enterobacteriaceae (NPE) and Pseudomonas aeruginosa from intraabdominal infections (IAIs) and urinary tract infections (UTIs).Methods. Broth microdilution MICs were determined for isolates collected in 22 European countries in 2015-2017 and interpreted using EUCAST breakpoints; imipenem-relebactam MICs were interpreted using imipenem breakpoints.Results. For NPE, 98.4 % of isolates from IAIs (n=10,465) and 98.5 % of UTI isolates (n=7,446) were susceptible to imipenem-relebactam, as were 42.4 % of imipenem-nonsusceptible (n=474), 98.6 % of Klebsiella pneumoniae carbapenemase (KPC)-positive (n=138), and 93.9 % of multidrug-resistant (MDR) isolates (n=4,424) from IAIs and UTIs combined. Molecular analysis demonstrated that two-thirds of imipenem-nonsusceptible isolates rendered susceptible by relebactam carried KPCs; 96 % (261/271) of imipenem-nonsusceptible isolates of NPE that remained nonsusceptible in the presence of relebactam carried metallo-β-lactamase (MBL)-type and/or OXA-48-like carbapenemases. Among P. aeruginosa, 94.4 % of IAI (n=1,245) and 93.0 % of UTI isolates (n=714) were susceptible to imipenem-relebactam, as were 74.4 % of imipenem-nonsusceptible (n=469) and 79.8 % of MDR isolates (n=595) from IAIs and UTIs combined. Among the 120 isolates of P. aeruginosa that remained nonsusceptible to imipenem upon addition of relebactam, 72 % carried MBLs. The distribution of NPE and P. aeruginosa carrying carbapenemases varied substantially across Europe, as did resistance to imipenem and imipenem-relebactam.Conclusions. Continued surveillance of antimicrobial resistance and resistance mechanisms, including the study of imipenem-relebactam as it approaches regulatory approval, appears warranted.
Keywords: Europe; Gram-negative bacilli; SMART; imipenem-relebactam; intraabdominal infections; urinary tract infections.