In vitro activity of imipenem/relebactam against piperacillin/tazobactam-resistant and meropenem-resistant non-Morganellaceae Enterobacterales and Pseudomonas aeruginosa collected from patients with lower respiratory tract infections in Western Europe: SMART 2018–20

OBJECTIVES: To describe the in vitro activity of imipenem/relebactam against non-Morganellaceae Enterobacterales (NME) and Pseudomonas aeruginosa recently isolated from lower respiratory tract infection samples by hospital laboratories in Western Europe. METHODS: From 2018 to 2020, 29 hospital laboratories in six countries in Western Europe participated in the SMART global surveillance programme and contributed 4414 NME and 1995 P. aeruginosa isolates. MICs were determined using the CLSI broth microdilution method and interpreted by EUCAST (2021) breakpoints. β-Lactamase genes were identified in selected isolate subsets (2018–20) and oprD sequenced in molecularly characterized P. aeruginosa (2020). RESULTS: Imipenem/relebactam (99.1% susceptible), amikacin (97.2%), meropenem (96.1%) and imipenem (95.9%) were the most active agents tested against NME; by country, relebactam increased imipenem susceptibility from <1% (France, Germany, UK) to 11.0% (Italy). A total of 96.0% of piperacillin/tazobactam-resistant (n = 990) and 81.1% of meropenem-resistant (n = 106) NME were imipenem/relebactam-susceptible. Only 0.5% of NME were MBL positive, 0.9% were OXA-48-like-positive (MBL negative) and 2.8% were KPC positive (MBL negative). Amikacin (91.5% susceptible) and imipenem/relebactam (91.4%) were the most active agents against P. aeruginosa; 72.3% of isolates were imipenem-susceptible. Relebactam increased susceptibility to imipenem by 34.4% (range by country, 39.1%–73.5%) in piperacillin/tazobactam-resistant and by 37.4% (3.1%–40.5%) in meropenem-resistant P. aeruginosa. Only 1.8% of P. aeruginosa isolates were MBL positive. Among molecularly characterized imipenem/relebactam-resistant P. aeruginosa isolates from 2020, 90.9% (30/33) were oprD deficient. CONCLUSIONS: Imipenem/relebactam appears to be a potential treatment option for lower respiratory tract infections caused by piperacillin/tazobactam- and meropenem-resistant NME and P. aeruginosa in Western Europe.